Thinking about a woman during sex.

I am married to a good man, and I am in love with him,but prior to him I was in a relationship with a woman who I loved deeply, but after some problems we decided to be just friends (she is my best friend) and we both are in the closet.

The problem is that every time I have sex with my husband all I think is in her and her body, I know is wrong but I can't control it. Thinking of her is the only way I can have an orgasm with him.