This "girls like jerks" thing is complete bullshit. People seem to be unconsciously attracted to certain kinds of people (not MBTI types, things like bad boy, nerd etc), and what will satisfy a lot of people is very different. Everyone has a certain sort of person that they will like, and everyone has a match somewhere. And please don't take that literally on purpose just to piss me off, I'm sure you know what I'm trying to get to.
Anyways, as for your friend's feelings, I'd say that he shouldn't torture himself with what he could have done, and just attempt to move on. The girl seems to want to have some form of physical contact to try to get over her previous relationship (from the limited information that I have), and if your friend didn't want a rebound then he made the right decision. He should still stay in contact with the girl. If she becomes available and isn't going to use him as a rebound, he should go for it. He shouldn't waste his time worrying about something he can't change.
My suggestion would be for him to talk it out with his close confidants. He should also find another girl to start talking to. Just my experience, when I'm going through bad times I have talked to my confidants about my issue, and I've also talked to another girl. For some reason, it just helps to do that for me, and for the people I've advised about this sort of thing.
Also, believe me. I know what I'm talking about. My best friend is an INFJ. The thing that helped my friend the most was talking to me and a few others that he held close, to distract himself in some way, and to talk to another girl or other girls. From doing this he's getting over his last relationship, that was very serious. It was 2 years with an ISTJ, and things didn't work out (wasn't a type problem, she had some psychological problems). He recently started talking to another girl, and they like each other. I also spend a good amount of time talking to him and hanging out. Your friend would appreciate your support I'm sure.