She Has Cheated On Me Twice!!! What Should I Do?

I have a girl who I love and we have been dating for two years now. I can proudly say I have never cheated on her, but she cheated on me twice and apologised. I thought of ending the relationship but I could not because I love her. But now, each time we are together, she feels like I am a stranger and cannot really relate. She is still in contact with her ex. What do I do? Thanks