I love my girlfriend dearly. I am just so confused. PLEASE HELP

I've been breaking my head trying to figure this out. it is eating me up inside and just making me sad and depressed.

I've been dating my current girlfriend for close to three years now. Ive known her since I am 16 years old and have had the biggest crush on her from the day I met her. I thought she was the hottest and prettiest girl I've EVER met. I wanted her from the first day but I didn't get the feel that she wanted me. Ive dated other girls until we met again about three years ago. all of the feeling Ive felt when i saw her the first time years before all came back and i made it my goal to go out with her.
after a short amount of time we have started dating and decided to settle down.
I was extremely sexually attracted to her as well as her personality.
at first, it was me trying to get her in bed. but then Ive slowly lost interest in sex with her. We are commited to each other and love each other more then anything but I am having a hard time wanting to have sex with her.
I have NOT lost interest in sex. I frequently pleasure myself while watching porno's and pictures of other girls. I fantasize about other girls that I know all of the time. I do not want to cheat on her with another girl but it is really hard. she is contently trying to have sex with me but i have no interest!. the weird thing about this all is that she is a beautiful and very attractive girl who gets many looks from other guys. but whenever I get horny, I'd rather pleasure myself then have sex with her.
I don't want to lose her. we are Best friends and i truly feel we are soul mates. My family loves her and we connect on extreme levels, just not sexually.
Can someone please explain why I am lacking sexual interest in a gorgeous and amazing girl?:surprised

You probably don't understand your sexuality. I would guess that (maybe subconsciously) you adore her so much that you feel exposing her to your basest drives would be a defilement. Maybe you've put her on a pedestal. Then the question is, why can't you put yourself on the pedestal? You think she's too good for you?

Maybe you're too selfish in bed, always concentrating on satisfying yourself. If you like her so much, you'll make it into a game of how much you can satisfy her. If she wants it, bro, you got to give it to her, and good. I think the best sex only happens in a relationship with someone you care about, because half the fun is enjoying the pleasure of the other.

Hey man, I know exactly how you feel. What I think the problem is is that you have known her for so long and have grown to appreciate her so much that you feel sexual activities might harm the way you look/feel about her. Maybe once that "hidden" aspect of her life (being her natural body) that you've never seen or explored is gone and you have officially seen everything about her, you will feel that it there is nothing more to be known or seen with her.

I can't really put my feelings and thoughts into words, but hopefully what I just said kinda makes sense to you? My advice is to not pleasure yourself for a few days, then start fore playing with her and try to get past your feelings and just do it. Maybe once you finally do it, these feelings will stop and you can proceed!