Not trolling. Throwaway because embarrassing. Asked elsewhere but think I'm not getting good advice.

I'm a pretty fit, reasonably good looking 24 yr old guy. I've been in a string of longer and shorter term relationships like most guys, with more or less success. My current girlfriend [23] is by far the hottest girl I've been with, and been with her for about six months. I mean "hot" both in looks (and in the way she keeps herself and carries herself) and in bed, she's very passionate. I'm starting to feel that I'm not good enough for her and it's doing a number on me.

First of all I can't really keep up with her in bed. She wants to have sex a lot more times than I do. When we do have sex I feel I'm not really satisfying her. She wants me to take charge and be more dominant but I'm really not comfortable doing that and I feel awkward trying. Also people joke that she's "out of your league," which I didn't agree with, but she IS very good looking and combined with these other things, makes me begin to feel intimidated by her. To add to this, there's the problem of a fetish I have. (No I'm not trolling and I made this throwaway account because this whole thing is embarrassing and what I'm about to say even more so). I used to get off at the thought of my gf getting banged by another guy. At first I thought this was just a passing fantasy and wasn't really important but being intimidated by the girl I'm currently with has made this fetish return and become more intense. I can't help thinking about her having sex with guys who are more muscular, badass, bigger dicks, whatever, all the corny stereotype things that go with this fetish (yes including usually imagining her with a buff Latin guy from my gym especially, we're both white). I know it's stereotypical and stupid but it turns me on like nothing else and it's interfering even more with our sex life. This on top of me being sexually intimidated by her and feeling I can't keep up is really doing a number.

I like this girl and want to stay with her for now. She's good looking not just physically, but a good person, and understanding. She doesn't really know about my fetish but is perceptive enough to know what I'm feeling about the other stuff and she's trying to "encourage" me that I'm a big stud for her. But that only makes it worse because I know it's not true.

I'd like some advice for how to gain some confidence, not think about my weird fetish anymore, and have a sexually fulfilling life with her. Should I be totally honest with her and tell her everything? How would you handle this.

tl;dr: Sexually intimidated by my GF and annoyed by my fetish, need some advice on how to deal