It does not sound like either you or she are ready for a good, committed relationship; in addition to all her cheating she is cheating on other people with you; I can't see that she will quit her ways or that you are a good influence on her or even for yourself? No one else can use you, you have to allow them to. I think you should work on your own self esteem and then find a partner that will treat you right, based on how she treats herself and others.