Colossus loses his cool when he sees Kitty with her new boyfriend, Pete Wisdom!
Colossus has just come back from Avalon, after having worked with Magneto there in hopes to protect mutants and perhaps convert them to Xavier's dream. He is clearly distraught, and it only gets worse when he finds Kitty Pryde kissing her recent boyfriend Pete Wisdom. Colossus attacks Pete Wisdom, beating him senseless until the team Excalibur fights back and subdues him.
After Colossus' rampage has been put to an end, he finds himself in a holding cell in Excalibur's headquarters. There he has separate conversations with Moira MacTaggert, Nightcrawler, and then Kitty about his return and behavior. Through these conversations, Colossus reflects on what happened on Avalon, realizes his horrible mistake in nearly killing Pete Wisdom, and comes to terms with things not being the way he had left them.