HI Alexandra-
<big hug> Well, I'm not going to get into the whole, how can a "straight" guy have sex with a non-transitioned tgirl and still claim that he's not gay or bi. All I can say is that orientation, like so many other things, is sometime fluid and circumstantial.
However, I will give you a warm welcome to TGS. It sounds like you have your feet under you and are comfortable, prretty much, with who you are. This is a great place to make friends, get advice and perhaps seek answers. No one will judge you or codemn you, which is not to say we don't have our little spats and disagreements.
Please feel free to join in on the various forums and chats. If you have any questions, please let me or one of the other mods know and we'll be glad to help out. Once again, a warm welcome.
Hugs...Joni Mari
"Be yourself, everyone else is already taken."
-Oscar Wilde