Yesterday, my bf brought up the possibility of a 3some with another girl. from there, it went to a guy, and from there he came up with me getting a strap-on and performing anal on him. what does that mean? is he bi? he's never been with a guy before...

no he isn't bi or gay he just wants to have a little adventure. So did you strap one and ride him good? I luv taking hubby for a ride every now and again. Did you do the 3some?

Naw it doesn't make him gay or bi. I mean he might be only he may know that. Just because he wants you to nail him like he's the girl doesn't make him BI or gay. Its more of a dominance thing. He probably wants to be dominated by you. I am actually in the middle of getting a strap on so my wife and I can do that. they have ones that stimulate the female while she wears it. I say have fun and don't worry about his sexuality.

Girls like anal, it's not unusual to assume that guys like it too. My husband likes it, but is ashamed of it. We have only done things with his ass when I caught him in the heat of the moment, but I know he wants me to get a strap-on. I didn't like the idea so much at first, as I am an extremely submissive person, but I have warmed up to it as time passed.

Sounds to me like he was trying to take a discrete path to asking you to fuck him with a strapon. Nothing wrong with that and it doesn't make him gay/bi or anything else other than a horny guy.
Are you open to any of his other suggestions?

No he just wants to feel it up his ass, no big deal lighten up and have some fun