As someone from the outside perspective, you're just gonna have to get over it. If he's really straight he damn sure ain't thinking about you. Do NOT try to pursue anything with him and just ignore it. There's a strong chance that not only will you get hurt but you will make him dislike you. A lot of straight guys are really sensitive when it comes to their sexuality and he will more than likely be completely creeped out more than anything.
The slim...
extremely slim chance that he would magically end up turning gay and falling in love with you is not worth the humiliation.
Plus if he has a girlfriend and she finds out you're out for ha man you are liable to get cut.