My girlfriend i broke up with made out with another guy and wants me back.?

This might take awhile so bare with me. We had been dating for 3 and a half years and were deep in love for 2 of them, until grade 12. We had less time together because of school but i still loved/love her. Eventually she broke up with me saying she wanted to be independent and still loves me. I was extremely upset and let her know that, but she just kept saying we'll be best friends! We'll still be together! If we go to the same university we can date again. She said she wasnt sad because we'd still be in eachothers life and that she blocked out the past 2 and a half years because if she thought about it she was so upset. A few weeks after this i find out that a kind of friend of mine and her friend since childhood were making out beside Toys R Us. They were spending alot of time together before she broke up and after we broke up and i trusted her and him not to do anything. Initially when my friend told me this i did not believe him and thought it was impossible for her to do that to me(he found out 2 weeks after the incident), she had told me earlier that she was going with him(a couple days before i found out), a friend of mine and another one of her childhood friends to visit McGill on the easter weekend. After i found out i feel like she betrayed me, and did not feel guilty because she continually went places with him during this time she stil lsaid she loved me and missed me and stuff. She insists this was the only time and says that she'll never talk to him again. She came to my house on the day that i said we were finished and the day after and was crying for around 7 hours insisting that she was sorry. I love her so much I just don't know if I can trust her, she wants to get back together with me as she know i wanted awhile ago for the last 4 months but i feel so unhappy whenever i think about what she did, and what will happen if she finds a guy who is actually attractive(hes average looking but she told me she thought he was gross a long time ago). I really wish with all my heart that she could make it up to me somehow and that I could forgive her but I don't know if i can ever trust her again. During the break up i felt like **** and after this incident i feel completely disregarded for, and that she didnt think about me AT all and that our 2 years together meant nothing. Now that she knows i know she feels guilty about it im 'sure' but i know i would have never found out if it werent for someone seeing her and I dont know how close their relationship was with eachother (she continually insists it was just one time). Again she promises she'll never talk to him (which i never wanted but i need something to trust her or something) and she keeps saying she loves me, which i believe she believes but if she did she never would have done that to me. Again, i love her so much and before this i saw my life with her. I know i may be naive but i know how she makes me feel when we were together. I need help on what to do, my friend told me to go with my heart(after he told me to break it off along with others but i insisted that I can't let her go even though i want to), but i did that once and got hurt. He told me this is my only chance to get her back and if i dont try i might forever regret it. I think she really wants for us to be together but i think shes also confused on who she is, i find her really smart and cute which might be part of the reason i cant let her go, I invested so much energy into this and i only wish that she had invested half of it back. (just in the last year, the previous 2 years were the happiest of my life). I don't know what to do, and again its just 4 months until university, then i dont even think she wants to do long distance. Thanks for reading this longgg post and i appreciate any feedback.