Advice please!

If you caught your man in the bathroom jacking off to porn in the middle of the night how would you react? I'm upset, but not sure if I'm overreacting to the situation.

edit: I guess I should've added that he tried to lie to me about what he was doing when I caught him and that is what bothers me the most. Also this is my first serious relationship and my first time living with my significant other, so lay off the hateful comments. I asked for advice not to be critized for the insecurities I have in my head.