Desperately looking for advice from people who have their heads screwed on straight.

I've been in a relationship now for 3 months with a wonderful girl in her mid 20s who is full of love, energy and affection. She meets me at my level intellectually and our relationship has been full of deep meaningful connection. We've travelled together and our relationship even started on the back of a strong friendship. We are pretty much in love and love each other.

However, although I trust her good intentions, she is shockingly naive about boundaries with other men. She will often meet one on one for hours, share details about emotional and sensitive topics freely, and perhaps most worryingly of all she is very touchy-feely (intense hugging, giving neck massages etc to make friends). Somehow, I managed to rationalize all of this away when I entered a relationship with her, despite feeling uncomfortable about it, and telling her how I felt. I got reassurance from her and I felt that she is trustworthy, so I brushed it all aside.

Last night she did something unforgivable. She told me a friend of hers, a guy, was travelling to our city and his accommodation plans fell through - meaning he had nowhere to stay, and he had no money. She asked if he could stay in the spare bedroom...I had my misgivings, but it was getting late and cold outside. I said ok.

My instinct told me that something was up and I could not relax. I felt angry, my body was tense. Sleeping next to her I felt revulsion that I couldn't explain. I confronted her the next day about him - straight up, if they had a history and if she slept with him in the past. She then admitted that they had a one night stand about 6 months ago.

I feel utterly violated and humiliated. That she could allow someone to enter my home, without disclosing that he was a sexual partner in the past, and somehow think it was ok...irrespective of the circumstances.

I don't have any trust in her judgement anymore and I have no interest in carrying on if it means my dignity and sense of integrity is violated. I feel foolish that I brushed aside my misgivings about boundaries in the past.

She feels mortified and says she will do anything to make us work.

I love her, but I can't trample on my values for the sake of feelings. I told her that I'm breaking up with her.

Please someone help me process this... What am I meant to do..am I doing the right thing? What happens if I take her back??