It sounds like your boyfriend is manipulative. He is using you to make himself look good and to get by easier in his life. Telling others that you are clingy when is depends on you so much is a way to avoid seeing that his behavior is actually what he is describing to others when he talks about you. He may feel threatened by you or by he feel the need to control you. He may also pick up on your feelings about yourself and want to take advantage of you. He seems to be a classic narcissist, where everything is about him and everything is someone else's fault.
He goes with these girls because one, he needs to be adored in order to feed his ego. Two, he needs to be the center of attention. Three, because he likes to control others and four, because he wants to push boundaries and see how much he can get away with. He may also be extremely insecure and having these girls, the more the better, is a way for him to feel attractive and wanted.
The girls probably stay with him because he is focused on them, even if it's only for a short time. Some people grow up with a deep sense of insecurity and need any attention they can get to feel better about themselves. Instead of trying to fix what is wrong with themselves, they look outside of themselves to others to give them value. When someone pays them attention, they grab onto it like a life raft.
But no matter how many girls your boyfriend is with, he will never have a normal relationship that means anything until he addresses his own issues.
If you want to stay with your boyfriend, you may need to be prepared to accept his behavior. He is not going to change until he wants to change. And right now he lacks the insight. When you want to get a certain response out of him, praise him in such a way that you do get the response you want. For example, if you want him to do a certain task, tell him that everyone admires the way he does it. Appealing to a narcissists ego usually works.
Try to keep your emotions out of your dealings with him. Narcissists often provoke emotional reacts in others because their behavior is so offensive and hurtful. Training yourself to not react and to remain neutral can help. Develop a few non emotional responses you can provide to just about anything he says to you, especially when he tries to provoke you. "I'm sorry you feel that way" is a good response to just about any comment. It leaves your feelings out of it, negates a reaction and keeps him from feeling he can get a reaction out of you.
The most important thing to do is learn what you can about living with someone who has a personality disorder. It can be very stressful and very trying on your self esteem. Along with using the resources I gave you, consider counseling. It will help you deal with the effects of your relationship on you and you can find ways to cope with the stress.