There are straight guys who enjoy sharing their sexuality with other guys. Enjoy them, God knows I have. Here are a few suggestions:
1) When it's going to happen, you know it's going to happen, just like when you meet a lady at a party or at a club. If the chemistry is right and sexuality is an ingredient then proceed while carefully reading the signs and signals (and warnings) he's giving you.
2) Be versitile. If you want to share your sexuality with a straight dude, you need to offer him the fantasy (both mental and physical) that he needs.
3) Do not be sexually dogmatic. I have found one of the things that inhibits straight guys from experimenting sexually is they have experienced guys who insist on telling them because they enjoyed a blow job or even got fucked, they are gay, and face up to it and admit it. In nearly every case I know of this is NOT what the curious straight guy wanted to hear when it was over. "Nice, guy, real nice." Is much more appropriate to the situation Also remember some guys start to freak out when there's another guy over them. Relax about it, lay on your sides, it's about having fun, not about winning an argument.
4) He's going to get up and go home either to be alone or to be with a lady. He's not looking for a long term partner or ever someone to wake up next to tomorrow morning, he's looking of a new and hopefully very satisfying sexual experience. If you really enjoy straight guys, this is what you should give him.
Use common sense, you should be able to stay out of trouble, not get hurt and have some far out sexual experiences with some very far out straight guys. But remember, like any successful sexual experience respect (no matter how it is acted out) is second only to horniness.