Sounds to me like the poor lass has low self esteem issues which must play havoc with her own well being at some level, if she is physically loyal to you then perhaps the relationship needs some more effort from both of you to help smooth things over, if you feel you cannot continue coping with her behaviour and you have discussed how you are feeling with her then perhaps it is time to move on but I couldn't recommend you do so without thinking long and hard about things. If you really love this girl and if she is worth going that extra mile then try to stick with it and maybe seek out some counselling for you both, once you turn your back on someone it is often too late to go back to them, I would consider how you can repair your relationship before giving up on her.