Single women vs Married Man love story, Who is right/wrong? What is right/wrong?

My best friend fell for a married guy who also loves her equally but he can't be with her bcoz of his marriage and a kid. Now they both have reached a point that they are emotionally too involved and attached to each other and can't leave eachother. Though he had already shared everything about his marriage and kid to my friend before they started dating and he did mention that he will never leave his wife as he said she (his wife) has gone through a lot in this marriage bcoz of him and she has never left his side no matter what plus she was raised without a father her whole life hence if confronted, she would never want that to happen to her kid, hence she won't leave him either even if he wants to... Plus he loves his wife and kid a lot. And he equally loves and wants my best friend and so he said he can be in this, ok to have a relationship with her but not in open it would be a secret life. Secret relationship/marriage.. That's all he can give to her. I have personally met this guy and he is genuinely a nice person but I don't want to judge anyone here because people have their own issues and reasons.. But I don't want to lose my friend in this too..

Now she is confused because she loves him a lot but she doesn't want a half life with him living in a secret and make her life limited not only for her but for her future kids (if they decide to have one). I have tried to make her understand in every possible way but she seems so attached to this guy she is finding it difficult to take a decision. And this is the first time she has got involved with a married man... I need a better perspective from anyone out there who is reading this so that some how I try and help her to understand... Please share your perspective to better her situation. Please throw some light.
Thank you 😊
Single women vs Married Man love story, Who is right/wrong? What is right/wrong?
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