Time to end long term relationship ?

From what you say, I would say its time to try to move on. It seems to me that you are her back-up plan. What I mean by that is that she is always looking for someone "better" than you in her eyes and that you will just always be there for her to fall back on if it doesn't work out with one of her "friends." This looks to me like a bad situation, where you are being denied long-term happiness by her and the "game" she is playing with you emotionally. I would try to move on and possibly seek the help of a professional to help you through this phase of your life.