is it cheating?

I've never thought of watching porn as cheating. but lately I've found a LOT of porn on my boyfriends phone. We have a 1 year old son and a 3 week old son and he tells me he isn't masturbating and he's just not in the mood but he doesn't know I've seen his browser history. What bothers me is that he would rather please himself and LIE to me about it then come to me horny and have intimacy. how would you feel about it?