with just his fingers, he can kill, be he does not, because he knows what dying feels like.
{in which he realizes that they are truly pitiful}
{and in which he contemplates why they are one of those living in glass houses}
Izuku breaking an arm or a leg it's nothing compared to what he will go through, he knew she was looking at someone else but his foolishness didn't let him see that. Now he needs to learn to endure it or he will be a walking stress time bomb.