What do I do in my relationship?

My girlfriend has been seeing and getting together with other guys with my knowledge. This has been going on for a while. I really really love her and don't want her to leave me so I was fine with her sleeping with other guys. Anything for her. I want to gaze in her eyes and tell her I love her and protect her. I have low confidence so I do not think I can ever find another gf in the future, what do I do?