Boyfriend likes gay things?

Alex
Okay so I've been dating my boyfriend for almost 4 months and I know he's bi. We've talked about his likes and dislikes sort of. All I know is he would like me to put a strap on and maybe fuck him in the ass. I just don't know if I feel comfortable with it tho because then he might like it a lot and want to be with a guy. I'm just scared he'll leave me for a guy. Plus I've never been with a bi guy, help?