<human>: About two weeks ago my best friend (we'll call him Jack) cheated on his girlfriend (we'll call her Crystal) by giving a woman oral sex for money. That day he had called me in a pinch about needing money to pay off a bill and he was short about $200. I offered him a few dollars to help him out and gave him ideas to help him. By the end of the day he had only gained about $80 and was still short. Later that night he called me telling me about his endeavor to get the money and that I was sworn to secrecy. I tried to forget about it but it started to eat away at me, I was supposed to have lunch with Jack and Crystal a week later but the night before I broke down in tears. I just couldn't look into Crystal's in the eyes knowing what I know let alone watch them kiss and be romantic (Jack found out he had a mouth infection the same week he cheated, which could possibly be connected). 

   On my end my friendship with Jack has deteriorated to the point where I don't want to be his friend anymore; he can be very manipulative and has tried to isolate me from most of my friends the last six months, telling me and trying to persuade me to end friendships because he has personal issues that were seperate, and in general a very disrespectful and misogynistic person who constantly pushes my boundaries and morals. Up until a few days ago I was planning to distance myself from him but due to a project I'm contractually obligated to work with him for 3 more weeks. Now I definitely want to end the friendship with Jack but I don't know to go about it or tell Crystal, she's been a great friend to me and has been there for some problems in my life.

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<bot>: my best friend cheated on his girlfriend and has spent the last couple of months pushing me away as a friend. Do I tell his girlfriend and how do I end my friendship while working together?