How do I go about tell my husband I'm gay?

I've been married for 17 years. I love my husband but I'm not attracted to him anymore and found myself interested in a female co-worker. My marriage as far as my husband is great. He is a wonderful man.

Do I tell him and end it? Do I have an affair? Do I ask him for an open marriage?

I don't want to hurt him but I don't want to keep up the charade that I am interested in him sexually. It's not fair to him and it's not fair to me.

Please help.