Boyfriend watches gay porn

We have been together for 4 years from 14-18. I know he watches porn but have never really cared and I've never been interested in what he watches. However, I went on his laptop yesterday he knows I do this sometimes and he'd left a tab open which was porn. I clicked on it out of curiosity really and it was a video of gay porn. Last night I spoke to him and he said ‘sometimes’ gay porn turns him on but he doesn't find them attractive. He said he started because he didn't want to look at other girls in case I said it was cheating

What do I do??