It sounds as though you are resentful of feeling like the secondary in the relationship. Are you the secondary or are you co-primaries? That may be something to work through in time.
Cindie was right btw. You and the other gf should be spending some time together and communicating with each other- not just with him. Have you spent time talking to her?
I think it's good that you considered her feelings and gave her 4 nights a week, but understand also that if you resent considering her feelings and you bottle that up you could say something you might regret.
She is a part of his life (as much as you are) and although in most instances I would say let them work through their issues together this concerns both of you. I would approach her and talk to her about the many issues you all have. Tell her how you feel that she gets more or better quality time than you, tell her that you know how hard this is for her and thank her for being able to accept you in her life, get to know her, etc. Most importantly, do NOT keep this secret from her.
Find time to sit down with the two of them and talk about this issue. How would you feel if you were in her shoes and didn't know? You would feel bad if she hid this from you. If nothing else, telling her yourself will build trust between the two of you.