Hi there,
you've probably already discussed the whole thing with your partner by now....
Either way..
If this girl really believes you are the father of your child then you are in the same position as any man who has had a thoughtless moment, and maybe fathered an unplanned child- gay or straight makes no diference as far as parentage goes.
If the girl is 3 months pregnant already, you are pretty much out of time as far as termination goes, and she must be planning on keeping the child. If she has waited this long, she has made the descision without you, which her right, but a bit infortunate for you.
At this stage, until it has beeen proved otherwise, you are the father of a child, and will have to factor this into your future.
Discuss it with your partner, as the decision seems to be made already, and see what you can come up with.
There is a big difference betwween being a father, and being a proper dad, and there's no reason why a gay man, or a gay couple, can't be either, or both.
You may eventually come to think of it as one of the best things that ever happened to you.
I'm a woman, but I didn't plan to have any children, I was taking every reasonable precaution to aviod it, to be honest- but found myself pregnant anyway, 3 years ago.
I know wouldn't want to imagine the world without my duaghter (now2and a half) I wouldn't change my decision to have her for anything. I am now married to her father, and expecting her little sister on 10th november.
I wish you, your partner, your child and your child's mother all the best, whatever happens. Every family is made up differently, there's no reason that you guys can't make it work, if that's what you want.