Porn 😐

My Fiancé and I have been together for a little over two years now. I've caught him watching porn before and we talked about it and it was bc I had been sick, I get that.. but I've caught him doing it multiple times now and I've asked him to stop and he hasn't. Now he tries to hide it from me, which I think is worse. Am I overreacting? I'm always down to have sex and pleasure him when I'm on my period but his sex drive has lowered and I always see porn on his phone. Why is he looking at other naked girls instead of me? I use to watch it myself, but now that I'm with him I don't have a reason to. It bothers me that he watches it all the time but is "to tired" for sex when I try.. and when I confront him he says he's not doing it..  😐