How do I confront mum about her love life?

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My mother has been a widow for 12 years and over the years I have seen her date different men who always break her heart. I think it is just about to happen as she is in love with a married man. His wife and many other people know about it and according to her he is in the process of divorcing his wife. However, it does not seem so as he always goes back to his wife even after spending days at our place. I am worried about her because she is so vulnerable and lonely but I know where this will end. I want to help but I don’t know how. I am 22 and the first-born. Please advise...{Opara J}