Can a man look at gay porn and still be straight?

Recently I caught my boyfriend emailing a personal ad on craigslist to a man trying to set up a sexual encounter. He's done this before but with a woman. We've tried some stuff in the bedroom that he apparently liked and when I saw this he said that he was nervous bc it felt good and he associated it with gay sex but never has been or is attracted to males and doesn't know what he was thinking. In the email he made it seem like he was really into gay porn and gay chats but now says it was all a lie. We have been together for 4 years now and I don't know what to do I keep telling him if he has any feelings like he might be gay to tell me and he keeps denying it and saying it was stupid and he was too scared to approach me about trying new things with him. What do I do?