The difficulty you're experiencing arises from you not putting yourself in her shoes:
- If she was very proudly a gay woman, then this would be very confusing for her (because, she simply isn't completely gay).
- if she made being gay part of her identity (who she thinks herself to be, the culture, the pride in being gay etc), then she may be having an identity crisis
- if she has many gay friends, they may be in her ear (so to speak) about sleeping with you
As a supposition, without necessarily relating to her - a rather high percentage of gay women sleep around lots in their younger years. ie. you may not be the only person she is sleeping with...which may be confusing her.
That said, it appears you aren't thinking much about your needs either. You appear to be hurting, but not saying anything...which is tantamount to saying it's acceptable to you. Putting up with this for too long will start eroding your self esteem. Self esteem enhances happiness (while lack of it always erodes the level of happiness). And every person under the sun deserves both happiness, and self esteem.
Sometimes, even when people are special to you, and even when they are not purposely kicking you in the guts...you need to say something to them (because you need to stand up for yourself).
She simply isn't the only important person in this story.