In love with my married friend

I am a lesbian and have only been out for a short while, but i have known this girl J for a while now. She is bi sexual and is attracted to me, we flirt and laugh and make each other happy, we have a physical attraction and can talk about everything or nothing. Its great and we really care for each other. But i care for her more than she does me

Heres the problem. Shes married and has been since Jan, but the marriage is on the rocks, he doesnt treat her right and she feels cold and alone. She is committed to working on the marriage til it cant be fixed but its hurting her and i cant bear to see it.

I cant let her go and i cant have her. All my nerves are standing to attention and tingling, i get butterflies and i just want to hold her and mend he cracked heart. But until the marriage is over i cant. What do i do? It hurts so much!