My moh is a Mistress and i Don't Know What to Do

Hey all, I'm stuck in a sticky situation regarding my MOH and I don't know what to do.

So about 8 years ago, my MOH had this passionate fling with this Romanian man, but he told her that he couldn't marry her because he had a duty to his parents and his culture to marry a Romanian/Eastern Orthodox woman. So he breaks up with my friend and goes to Moldova gets married to a "proper woman" who is Romanian/Eastern Orthodox, and brings her back to the United States. Just a few months later, he rekindles his relationship with my MOH. The two of them meet and share another passionate night and he tells her that he can't divorce his wife because he's committed to her. So she becomes his mistress and the two of them essentially enter into this long-term affair, which has been going on for the past several years. They meet once a month and have sex and share all the intimate details about their lives: my MOH tells him about all the men she dates and how they don't compare to the Romanian man. He tells her about how miserable he is with this wife and how he is sexually unsatisfied with her.

My MOH and the Romanian dude have been at this for years now. She lives in Portland and he in Seattle. Once a month, she'll drive up to see him. They meet in various hotels across the area. The Romanian man's wife has no idea about any of this. He is an Uber driver by profession. The wife thinks it's business as usual when he leaves the house.

While I could once turn my back to this, I can't do it anymore. Since my MOH returned her leased car a few months ago, she now buses up to Seattle from Portland and has me drive her to and from the various hotels where she meets "her man". She's always elated to see him and tells me all about the fantastic sex they had together. Lately she's been wanting to have a child with him and lines up her "visits" to coordinate with her ovulation cycle. She tells me that she doesn't want to be a home wrecker though, because the Romanian man will want to take care of this child with her. She is perfectly content with her relationship with him, as is he and has no plans on saying goodbye to him.

I don't know what it is, but lately I just feel so uncomfortable even talking or texting with her. Perhaps it's my upcoming nuptials. I think about his wife, who thinks the world of her husband because he's hard at work, earning money for the family, while she watches their two young children. Perhaps it's the fact that I am now having to take part in the wrongdoing, since I am the one driving her to and from the hotel. But I no longer want anything to do my MOH. Am I just overreacting? Should I just accept that these are facts of life and cope? Or should I ask her to not come to my wedding anymore? She hasn't made any expenditures on her part yet. I think it's also worth noting that I've been cheated on several times in previous relationships. On BF was basically doing a "test run" with me and another girl. Three months into dating, he told me all about it and said that he liked the other girl better. Another BF couldn't stand being alone for more than two nights in a row. I travel for work on the weekends and he'd utilize that time to sleep with other women. I really want to be objective about this situation, but I don't think I can. I so badly want to follow him home and tell his wife about it.