I need sum amazing thoughtful relationship advice?

I am 20, my girlfriend is 19. She has lied to me a lot in the past but has never cheated...we have been going out for 1 year and 7 months. I just found out she madeout with a guy she works with that i found out about on my own without her telling me. Infact she tried to cover it up so much lying about what she did/where she was. She is willing to sacrifice a lot we have been broken up for about a week now and everyday she has begged for me to take her back because she says she loves me and misses me. Is this forgiveable? Would anyone take her back? I want some advice as to what people would do in this situation. I want some advice because i told her we should be friends until she proves to me that she can be in this relationship and try. However, because she is a liar and a cheater i wonder if it might always be like this? what do you all think?I need sum amazing thoughtful relationship advice?
I would give it some time. She was unfaithful, and broke your trust. Trust is a big part of a relationship. If after a while, you think you can trust her again, I'd say you can take her back--but it's up to you. If she's the type of girl who will lie to you and cheat on you, do you really want to be in a relationship with her?