Well, here are some of the best answers from the original posts, along with some heartwarming new ones from the comments section:
1. "One of my husband's favorite songs is a love song about a girl, and he said he'd never pictured anyone while listening to it before, until me. That's when he knew."
2. "A week after our first date, I got knocked over in a bike accident and ended up at the hospital with a broken neck and a fractured spine. While visiting me in the hospital, he wasn't allowed anywhere near my head. So since he couldn't reach my hand, he held my foot the whole time instead."
3. "My wife and I met during our first year of college, and I had been dealing with insomnia for months. I couldn't fall asleep without medication and even then, it was difficult to sleep through the night. Well, my wife and I had started a sort of 'friends with benefits' relationship, and the first night she slept over was the first time I fell asleep without medication AND slept through the night. I realized the next morning that I was falling in love with her.
"Now, almost a decade later, we are married with a beautiful daughter and a son. I can't imagine my life without her in it. And I don't want to."
4. "My little brother has severe autism and even though he is a grown man who is 6 feet tall and weighs 200 pounds, he behaves like a child and wants to be treated like a child. Well, one day, my then-boyfriend and I took him to the park, and he proceeded to push my brother on the swings for a long time. That was the moment I knew I would marry him someday."
5. "I was on a date with this girl I really wanted to impress and not only did I bungle the night by forgetting my wallet at an expensive dinner, but I also lost my car in the parking garage! I was embarrassed and mortified, and after 20 minutes of running around this parking garage level by level, I could feel her glare and irritation on the back of my neck. I just knew she was thinking that it was the worst date she had ever gone on...
6. "I was at work when I found out my best friend John died in a car wreck, and I went home to my girlfriend and cried on her shoulder for an hour. Well, not only did she go to his funeral with me, but she also walked beside me as I performed pallbearer duties. I knew right there that if she was willing to literally walk beside me through one of the most difficult times in my life, I wanted her beside me for the rest of my life.
"If we have another child and it's a boy, we're going to give him the middle name John."
7. "My parents are immigrants and work minimum wage jobs, and her parents are well-off and own their own business. I was ashamed to tell her what my dad did so when she asked about my parents, I dodged the question. But she knew what I was doing and said, 'You should never be ashamed of your parents. They've worked so hard to get you where you are; I'm so proud of them.' I couldn't help but break down and I knew right then and there that I would marry her.
"I know it sounds kind of small but to me, it defined her character. And I have no regrets."
8. "On the fourth date, when she invited me up to her apartment and I saw that her Star Wars Lego collection was even bigger than mine. I knew right then and there."
9. "My boyfriend and I started getting serious a few months after my mom passed away. One day, I mentioned in passing how my mom used to braid my hair in different ways — even when I was in my 20s — because I could never figure it out. Well, a few weeks later, my boyfriend asked me if he could braid my hair because he had been watching YouTube tutorials. That's when I knew."
10. "I was working on commercial fishing vessels and couldn't watch the NHL playoffs, so she watched the games and texted me updates. That was the moment. When she was willing to learn the rules of hockey for me."
11. "My husband told me it was when we were playing Monopoly on a board he said he'd never lost on, I beat him, and I celebrated by singing, 'It's my game now, BITCH!'"
12. "We were at brunch when a vet with a disability came over and started a conversation with him about his motorcycle jacket. My man had just gotten laid off but he looked at his budget and bank app right there at the table to figure out where he could cut a corner to pay for that vet and his wife's meals. I almost cried."
13. "We had officially been together for a few weeks when I decided to have the conversation I always stressed about: That when I was 16, I was told that the likelihood of me carrying a child to term was slim to none. This had been a deal breaker for a few guys I had dated before so I didn't want to waste his time. But he responded, 'We'll get them how we're supposed to. Whether we adopt or by some miracle we have biological children, they'll be ours.
"I knew then that we were in this together, no matter what life had planned for us. Almost six years later, we’re happily married and after two pregnancy losses, we had a rainbow girl and are expecting a rainbow boy any day."
14. "I had gone out with her and a bunch of her friends, and she got a little drunk so I took her home to make sure she got there OK. She asked me to stay because she wasn't feeling well so I spent the night with her while she profusely apologized for drinking too much. I woke up in the morning with her cuddled up to me on my right side and her golden retriever cuddled up on my left side, and I knew I was right where I was supposed to be."
15. "When her boss messaged me to tell me she always knew when my then-girlfriend was texting with me as opposed to anyone else, because she would always be smiling."
16. "When I first met my now-husband, I noticed that animals gravitate to him. And not just pets. Once, we were sitting in a park and a flock of young ducks wandered over and circled around him, one even climbing on his leg. This happens all the time — dogs, cats, birds, squirrels. He's like a Disney princess! I figured if they trusted him, I should too.
"Twenty years later now, I was right."
17. "I was about to buy one of those gimmicky baking pans that make all of the brownies edge pieces, when I remembered that my boyfriend always ate the middle ones. So I asked him if he really hated the edge pieces because I really wanted to buy the pan and he told me to go ahead because — as it turned out — he liked edge pieces better too! He'd noticed early on that I always ate the edge pieces, so he ate the middle ones so I could have them.
"He did so without me even knowing it was for me, just because he knew it made me happy. I bought the brownie pan and I married the guy."
18. "I had a 3-year-old daughter from a previous relationship that ended before she was born. Well, my now-husband and I were having dinner with her fairly early in our relationship when she looked at him and asked if he was her daddy. I panicked inside and thought that would be the end, but he just smiled at her and said, 'Not yet.'
"We got married a year later, and he adopted her shortly after that. He’s the only dad she’s ever known."
19. "We had a major blizzard that left my backyard filled with so much snow that my dogs couldn't use it anymore. Well, one day, while I was in the shower, my boyfriend shoveled paths for my dogs to run along and I came outside to see him running along with them."
20. "He would tell me I was beautiful and when I said, 'I wish I could see myself through your eyes,' he responded, 'You would never stop loving yourself.'"
21. "I once had a boyfriend who was embarrassed by me at every turn. And once when we were shopping, I heard a song on the store radio that I liked so I did a little foxtrot down the aisle. Well, when I turned around, my boyfriend was gone. I looked for him for 30 minutes, and then I went outside to see that the car was gone too! That jerk had just left me at the grocery store and wouldn't even answer the phone when I called...
"Well, later, I was dating a new guy and we happened to be at the exact same store when the exact same song came on, and I resisted the urge to dance. But to my delighted surprise, my new guy swept me up into his arms and danced with me. That's when I knew he was the one. And 15 years later, we still dance in the store together."
22. "I thought I was going to have to do the 'walk of shame' from his place at 6 a.m. one morning after we'd been out, and I was putting my dress back on when he got out of bed and put on jeans and a dress shirt to walk me home instead."
23. "My husband says it's when he asked me what time it was and I responded, 'It's Howdy Doody time.' All of his other dates gave him the actual time."
24. "I told my now-husband that I was bipolar very early on in our relationship. A few days later, he asked me a very detailed question about how my mood swings manifest. I looked at him, questioningly, and he said, 'I did a lot of research online and I know it's important.' Melted my heart right then and there."
25. "My dad died a month ago at a routine hospital visit and we had just signed the DNR when my husband walked into the waiting room and immediately took my mom into his arms. That's when I realized it isn't just me he loves and cares for.
26. "When we were chatting about amusement parks and he said, 'I love...Universal Studios,' and I realized that I thought he was going to say, 'I love you,' and that I wished he did."
27. "My husband won my heart when he jokingly called me an asshole on our first date. I had been internet dating for a while and first dates were usually stiff and felt like job interviews. So it was refreshing for someone to be authentic.
"I felt like I knew him well as soon as I met him."
28. "We were visiting his parents in the Bay Area and just as we were leaving, his mom — who was very ill — asked him to cut her toenails. Most men wouldn't do that in front of a new girlfriend but he just went into her bathroom, got the clippers, and cut her nails. I knew that if he took care of her like that, he'd take great care of me. And he did."
And lastly...
29. "I asked my husband when he knew he wanted to marry me and he said it was when I helped him insert a suppository into his anus. So, you know, romance is a spectrum."
Some responses have been edited for length and/or clarity.