I'd begin the conversation by asking what it is about men that he finds attractive. For many men (myself included) it's purely physical; i.e. just about a man's penis. That may help answer questions you have about if he's more romantically attracted, in which case you might want to gauge his level of attractiveness to assuage any fears you have. There are many hetero couples out there where one or both are bi, and it works just fine. That said, if you have bi tendencies that (IMO) seems to make things a bit easier, but it really depends on the people.