I am a compulsive cheater?

Hypnotherapy could help. Or one of those hypnotists that do so called regression to a trauma that led to your current behavior; once you understand that, then is easy to confront the problem. Otherwise as you said, telling you to stop doing it won't help you much.

First of all, there's a fine line between nymph and slut, lol. Nymph= good, Slut = bad. But ne ways on the more serious side:

do you have problems with your father?
Were you old(er) when you lost your virginity?

If you say yes to either of these, then there's your problem. It seems to me its just an act of attention, and I know what you mean. I too consider myself a nymph and yes, I have cheated on very one of my boyfriends too. The only way to get rid of the issue is (seriously) don't be in a relationship or see a therapy*.

You can go see a therapist or join a sex addicts help group. You should do that first. Then you need to gradually learn self control. I think another part of it might be your insecure. Could you be cheating because your afraid of commitment? But I highly suggest you don't get into any serious relationships if you really don't want to hurt anyone. Find other things to do, hobbies or something. Also, if your really addicted to sex, try porn, masturbation or something else to satisfy yourself instead of finding some stranger to do it with. But I really think you should see a therapist, or possibly talk this over with a person you can trust or maybe a parent. Just be safe.

Find a group. Like AA, but only CA. I'm sure they have supports group for things like that. Maybe you should look into getting a therapist. I know they are expensive but they might be able to help in the long run. Don't get a man though! :) Research online where you can get help. In this kind of situation, it doesn't seem like just talking to one of your friends is going to help. You need other people who have this problem too and understand what you're going through. Stay single.

You sound like someone I know so very well and it doing it now to a really nice guy who is in the military and he is going to be hurt so bad, and away somewhere where he can do nothing about it.
VERY SAD

Ok don't no if this is the kinda help you want but you simply need 2 find sum1 you actually really care about. Once you care about sum1 so much so you won't wanna hurt them and also whoever he is has 2 have a real high sex drive 2 keep you occupied. Until then I don't know what you can do
Good luck