I'm pretty sure that my girlfriend isn't aware that I'm married to another woman.
Wow, has she ever asked you if you were married?
No, in fact I don't think it has ever really crossed her mind.
You not telling your girlfriend that you are married is you lying to her and that is wrong. Make a choice about what you want and be honest.
I feel like I'm not ready for this.
Ready or not, it's hurtful and immoral to cheat and lie to others. It's an uncomfortable situation, but its time to be mature and respect the feelings of these women who are being lied to and deceived.