The line is "he promised me a mate". That can be taken a number of ways, which I believe is intentional. In fact, I'm sure someone feels quite clever about it.
I'm pretty sure the mate was suppose to be the boar that you see in the bushes when you meet Astarion. (the one you see dead later)
That boar has a male voice, so I think not. I do understand that animals aren't necessarily heterosexual, but the word "mate" when used as a noun implies reproduction.
