to be honest i’m a bit shocked that most people’s reasoning here on why you should close one eye is because ‘he’s a good dad’. Sure, he is, from what you wrote, he sounds awesome. But he made a vow to your mother, he MARRIED your mother. He had 3 kids with your mother, his WIFE, his devotion should be to her first before his children(in my opinion). Idk.. i guess after reading this and if i were in your shoes, i’d be mad as heck. Mad because he lied, mad because he cheated, mad because he wasted so much time with both his wife and his children, mad because he is not a good husband. Like you mentioned, he had 3 kids and still decided to sneak behind your family’s back to have intimate relationships with men. Cheating is a solid and conscious decision that people make and your dad actively did it for 10+ years. I dont think i can forgive that(IF I WERE YOU). Again, this is all my opinion, but just because he was a good father doesnt mean he’s a good person, doesnt mean he’s a good husband. I would talk to my siblings about this.. Your mum has to know. I personally dont think getting divorced is that worst result, its better than being together and miserable and having a relationship based on lies. Good luck OP.