When I read that passage in the book, my impression was that an older girl (maybe the gang leader who spat in boys' mouths, ewww!) seduced him when he was a naive juvenile and convinced him to put out while she did "nothing." She destroyed his flower-like life, not once but twice. It wouldn't make sense if Moz was doing the seducing, as he clearly wasn't into it. But then, if she did "nothing," how did she get him to put out? Or maybe he was curious and the experience didn't meet his expectations.
As for being disgusted with the vag., that's not so weird is it? If you have a vag. do you ever get sick of changing tampons? LOL. Do you ever wonder why dudes would be so eager to make out with it? LOL. Look at CG: she's using some kind of device to prepare it for Moz. LOL. What I am saying is, this passage says more about his pre-sexualizing experiences than it does about his sexual preferences or what he thinks of women.
I do think that Moz may avoid the "pretty girls" (they make graves?) for fear that they will try to seduce him (well, that's what I thought when I saw one of his female assistants a long time ago), but that's all because of an early experience where he was most likely pressured by an older girl who clearly had her own issues.
Just speculating. 
