So for example: I love another girl... but she is in love with my girlfriend? Did I read this question correctly??

the one you love is gay? then there's nothing u can do unless u get something done

if you are in love with a girl who is in love with your girlfriend then you should: 1) leave your girlfriend because you are no more in love with her and so there is no sense to continue with this relationship because it will end up with a lot of lies and 2) forget the girl you are in love with because she isn't in love with you and also because visibly you've got the same tastes and she can't like you, a man. Get out of that chaos and in a while you'll feel relieved.

If all three of you can be honest and mature about the situation, it should not be a problem. Read this, for a start: http://en.wikipedia.org/wiki/Polyamory With more details, I might be able to give more specific advice.

there is certain ruls there, you can't and shouldn't do anything about it.find another one to be in love with