Lost in a relationship?

My girlfriend and I have been dating for 7 years we are engaged but recently I found out she had been talking to and messing around with another guy who is also a co worker with us both. We had a huge fight and after some time we both still wanted our relationship to continue. As the owner of business we work at I have to still be civil towards other guy but I am bothered by him and her still speaking at work even tho it's only about work related things I still can't shake being jealous. This in turn has created problems cause I will be upset or mad towards her. I just wanna know how do I handle this situation? I understand I need to trust her again but I don't know how when she still talks with person she cheated on me with

Lost in a relationship?
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