15. When Thor failed to lift Mjolnir. (Thor)
14. When Thor decided to sacrifice himself to save innocent people from the Destroyer. (Thor)
"Brother, however I have wronged you, whatever I have done that has led you to do this, I am truly sorry."
... Then Mjolnir returned to him and he once again became an invincible demi-god, but that's another story.
13. When Tony flew a nuke into space to save New York City, and tried calling Pepper in what he thought were his final moments. (The Avengers)
12. When Loki stabbed Thor... and proceeded to shed a tear. (The Avengers)
If you hadn't noticed that before, good luck handling the new-found Loki feels.
11. Loki talking to an illusion of his mother. (Thor: The Dark World)
He was forbidden from ever seeing her by Odin. Thanks, Odin. Great parenting.
10. When Agent Coulson "died". (The Avengers)
The fact that he didn't really stay dead knocked this one down a few points, but it was still a tear-jerking scene at the time!
9. When Loki "died". (Thor: The Dark World)
For ten whole minutes, we were afraid this might be the end for Loki (Again, we all know how long that death lasted).
8. When Bucky Barnes fell to his "death". (Captain America: The First Avenger)
Seriously, though. Does anyone ever stay dead in Marvel movies?
7. When Steve found out who the Winter Soldier was. (Captain America: The Winter Soldier)
Can you imagine finding out your best friend, the best friend you thought was dead, is a deadly assassin on a mission to kill you? And he doesn't even remember who he is?!
6. Captain America's last conversation with Peggy before his plane crashed. (Captain America: The First Avenger)
"I'm gonna need a rain check on that dance."
5. When skinny little Steve jumped onto a grenade in order to protect everyone else, unaware that it was just a test. (Captain America: The First Avenger)
4. "End of the line, pal." (Captain America: The Winter Soldier)
3. When we finally saw Loki as he really was. (Thor: The Dark World)
There are no words. Only tears.
2. "I could have done it, Father! I could have done it! For you! For all of us!" (Thor)
It was in that moment that we realized how terribly, tragically misguided Loki was in his attempt to prove himself "worthy" to his father... and what a terrible father Odin was. GREAT JOB, ODIN. A+ PARENTING. EXCUSE ME WHILE I WEEP.
And... possibly the most heartbreaking moment of all...
1. Bucky didn't know himself... (Captain America: The Winter Soldier)
... BUT HE KNEW HIM. After 70 years of being tortured, repeatedly mind-wiped, and trained as an assassin, there was one person from his past life whom he never completely forgot. If that's not enough to break your heart into a million pieces, I don't know what is.
OK, I lied about the no Guardians of the Galaxy thing. BONUS moment:
WE... ARE... GROOT.