<human>: Can you summarize the given text in a few sentences?

I'm a 21/f in my first relationship, so I'm new to all of this. My boyfriend hangs around with another girl a lot, and it makes me uncomfortable. She puts out a lot and is obsessed with sex, one of those girls who never stops talking about it and proudly refers to herself as a slut. The thing is, I'm not sure about the details but she's actually not fully biologically female. My boyfriend let it slip so all I know is that she's not fully female (very obviously though, I thought she was a transexual from the moment I met her). 

Another thing is, she has told him that she's in love with him, and has kissed him before (she claimed she didn't know we were dating at this point, could be true though). I trust that he won't fool around with her but I don't trust her the slightest.
I just feel a little bit thrown to the side sometimes, like he goes on "dates" with her, buys her dinner, and sleeps over at her house (slightly more complicated than it sounds - he works for her filthy rich dad out of town as a gardener, so when its too late to bike 1.5 hours home, he stays the night). Last weekend him and a bunch of our mutual friends went to a fancy dinner together and I wasn't invited for some reason. I saw the pictures of it and she was invited and was hanging off his arm, sitting on his lap etc.

He sees it as innocent because she's a bit of a social outcast (by her own doing, she's a downright bitch) and he's trying to help her make friends and stuff, and he assures me that he's not sexually attracted to her, which I believe as she's not fully female and he's pretty hetero. Basically this situation would be okay if he was hanging out with a guy all the time, it would be inappropriate if he was hanging out with a girl all the time, but in this case it's a transexual so... is it okay? I don't think it is, but he does.

What do I do? Well, I tell him of course. But what do I say?
<bot>: my boyfriend hangs around with a transexual girl who wants his peen, it makes me uncomfortable, what do I do?