Any advice is very much appreciated as this is a complicated situation for me. My GF of three years was married before we met and she was a serial cheater during her whole marriage. One of the guys she would mess around with was her landlord at the time and they’ve stayed in contact since she moved out. When I was finally told the truth about her past she was very determined that this guy was a very close friend and important to her life and will either be part of her life or I will not. I agreed that if he’s that important to her then she can keep him around, but no alcohol with him, no excluding me from any social meetings and no staying at his place. Basically coffee catch ups that I would be invited to. She’s literally just told me, because she forgot to mention, that she’s booked train tickets to go and see him tomorrow morning and there’s nothing to worry about, it’s all fine. I wasn’t invited at any point and have still never met this guy.