1. You're constantly looking for your favorite shirt or underwear, only to realize you left it at their place.
2. ...but that's OK, because your wardrobe magically doubles.
3. And all of a sudden you have access to twice as much food.
4. Your dental hygiene improves considerably.
5. No matter what your opinion of sports, you find yourself genuinely hoping your significant other's team wins.
6. You've accidentally ordered food to their house at least once.
7. And you've accidentally tweeted/Facebook'd/whatever'd from their account.
8. Your Netflix recommendations get completely mixed up.
9. You start to appropriate the other person's pop culture knowledge.
10. And their booze knowledge.
11. And they start to like the stuff you like too.
12. You find yourself using their products (some of which you never knew existed) in a pinch.
13. (Which is why you have to buy duplicates of all your important toiletries.)
14. Your key ring weighs like five pounds.
15. All of a sudden you have someone who is contractually obligated* to make you coffee when you're hungover and rub your back when it aches.
Although (clearly) you should be reciprocating.
*like, pretty much.
16. You *really* start to care about getting your side of the bed.
17. You have to explain all your kind-of-murdery-looking grooming tools to each other.
"I promise, it can't come to life during the full moon and rip your soul from your body."