Married to a man, secret affair with a woman

I am a 36 year old woman, married and I have an affair with a woman. Nobody can know and nobody knows!

First we were just friends but that changed and now she means everything to me. I never thought I would end up in an extramarital relationship. I also never thought of myself as a lesbian. Although it never really worked out with sex for me. What a difference with the sex I experience with my girlfriend.

Nobody knows how torn apart I feel inside, I feel so lonely and misunderstood. Is there anybody that understands me?

I cannot break up with her, she is everything to me. But I also cannot go on like this. I cannot imagine I will ever come out to family about this. Not possible. Never. They will not accept it.

I am stuck in this situation. What should I do?