Is it lust or do I really want to be with a woman?

Ive been wanting to get this off my chest for a long time. I cant figure out if this is a lust, a desire or if I am a Lesbian.
When I was 12 my Stepsister would make me have sex with her, she would have me perform oral sex on her, kiss her and hump her. This went on for three years without me telling anyone. When I turned 16, I noticed I started to develop feelings for girls, I had major crushes on girls in high school, I started masturbating to naked women in magazines. I notice when I got older I could only watch Lesbian porn, straight porn never turned me on. Lately whenever I see a woman walking down the street I cant help but to check her out, the way she walks is a turn on to me & I find myself sneaking glaces at her butt and boobs. Ive been married once and have had boyfriends but through out my relationships, never once was a sexually satisfied, Ive always had this desire to have a woman in bed watching while I have sex.
I am 30 and still can not figure out if I want to be with a woman or not. Could my feelings for women have developed from what my Stepsister had me do to her or is this just a desire that I want to fulfil?