Can you ever get through a betrayal with a partner?

Amy
My girlfriend and I had been together for 2 and a half years but were going through a rough patch. We lived together and had gotten engaged a few months before but everything changed when she got a new job and was working far too much. We broke up but still had every intention of getting back together. We still text every day after we broke up, even though sometimes it was just to argue. We had gone a few days where we were arguing pretty bad but then a few days later, things changed and we were really loved up again. I had planned to go to Spain for a couple of months to give us both some space to breathe and really appreciate eachother. Before I went, we became really close again. We were going on dates, sleeping together and it made me realize everything I loved about her. I only lasted a few weeks in Spain before I came home but when I came back, I found out she had slept with another girl she works with whilst we went through the bad few days of arguing. That is why she was so loved up with me suddenly again before I left for Spain. She said it's because it made her realize how much she loved me and she'd do anything to make it up to me. I am madly in love with this girl but I am disgusted and so hurt by what she has done. The fact she could sleep with me a few days later like nothing had happened makes me feel so gross but she has admitted everything she has done is wrong. I'm just so confused and hurt and I don't know what to do. Have any of you guys stayed with your partner after a betrayal and gotten through it? If so, how did you forgive and forget? X