In as much as you love her, and you do -- It sounds like this is not the best situation to be in at this time in your life.    It also sounds like she goes from man to man and if you cannot totally trust her, and if this is true, then I agree with you, you really do want out.  It sounds as if you are ready for a more serious relationship, and she is not ready for that -- evidenced by the fact of how she acts and what she has said to you.  Keep in mind, that the both of you are still very young and being that relationships are so complicated today, "Do you really want to be that serious just yet anyway?"  And I say that, because, as your life developes, you will continue to meet more and more people, so think about getting involved (seriously invloved) with the right person -- when she comes into your life.