Is my boyfriend gay?

Well, I’ve had the same boyfriend for almost four years yet we have never had sex (he says til we’re married). Also, the other day I came home and I saw him talking to his best friend on the bed. He assured me there was nothing going on, but I’m starting to have my doubts. And today, I looked over his shoulder and he seemed to be looking through some interesting pictures of his “friend”. He told me this was a dare they had going on or something like that…
Anyways, I really love this man, but what do you think I should do? By the way, I already tried talking to him about it and he simply denied it. Thanks!