This is a video of Bellamy from the 100 crying to Clarke about how he thinks he's a monster. Actual crying starts at 1:35, but I would watch the clip from the beginning for context, and it's not very long. For me, context tends to be very important.
https://youtu.be/usY8C4LAm80

Sorry about the 100 spamming, but here's another video of Bellamy crying when he heard his sister died. But Clarke actually isn't in this one for once. Yay. Also, the crying doesn't start until 1:30, but I would watch the whole thing for context.
https://youtu.be/0l_9G316_0U

This clip is also from the middle, like, seven seasons later. This one is more comedic, but still works. In the episode, Axle is being comforted by everyone because they think he's sad. He then stands up at the bar to tell everyone that he's okay, but ends up breaking down in front of them instead. He starts crying at 0:25.
https://youtu.be/Wre-U1P-xHo

This clip is the famous clip from Good Will Hunting, where Robin Williams' character tells Matt Damon's character that "It's not his fault", where Matt breaks down. The crying starts at 0:35.
https://youtu.be/yzb726TP-OM

This is a clip from the Office when Dwight starts crying because he wasn't invited to Michael's dinner party.
https://youtu.be/BspsqByKulc