I dislike assigning something like that in strict terms; sexuality is fluid and things change. I also dislike the term bisexual because of the inherent forced dichotomy in the term. I suppose the closest term I can come up with for Tony is pansexual. He's a live and let live kind of guy and when it comes to sex it's all good. Girls are easy and convenient for him, we know his uncle, and probably father, taught him a lot of his womanizing ways so he plays it safe and sticks to what he knows. I think it probably took a while for him to realize that he was attracted to men, as well, and that he's actually alright with that. I'm sure there was a freak out in there somewhere. As for now, he's comfortable in certain social situations and doesn't like to be uncomfortable, and he never got comfortable with the social rules involved with hitting on guys (beyond clubs and such) so he just sticks to easy one night stands. I think before Tim there probably wasn't really anyone he ever wanted for more than the one night or so. There's friends and there's sex and he was happy keeping them separate. Yeah, he wanted Tim but they had to work together he's off limits, except Tony still wants him and that confuses the fuck out of him. I think Jeanne was a kind of test drive; it was uncomfortable and unwanted at first but he found out he was capable of having a relationship. (I'm gonna go with the semi-stockholm thing, too, as far as actually being in love.) After Jeanne Tony had to sort out his feelings but in my personal canon they got together sometime around then. Tony still has trouble accepting that he wants more than sex from Tim but he's happy and he figures if it works why mess with it?

EDIT: Having said this I think its important to say I think Tony self-identifies as straight. Like any trait or title there are internalized social expectations that go along with it. To most people 'gay' is more than just a preference in sexual partners, it also allows for interpretation of behavior. True, you can be Jewish without being religious but it is assumed that you follow certain cultural mores. Same goes for being gay, bi, or straight. Calling oneself gay is likely to be reflective of a small amount of culture as well as sexuality. I cannot see Tony actively expressing himself in any way other than 'straight', regardless of his choice in partner, mostly because this is what he is comfortable with. For all his talk his personal life is likely a very stable, and elaborate, construction.

I think I'm done.