Should a mother become itimate with her daughter's ex lover under any cirstance?

I dated an older married man for three years off and on. I am 32 and he is 50. After I realized that the divorce was not going to happen I ended our relationship. Then he became friends with my mother all of a sudden. My mother hated him initially because she knew we were seeing each other and he was her age but she would put her feelings aside because I am an adult. She would just turn her nose up when she seen him as if he were a child molester. Now I haven't spoken to my mother in 2 months because the man I slept with for three years is now banging my mother and he is always at her house. This ordeal has drove my little brother away, he lives with me now becuase he can't stand to hear the sounds of love making knowing who it is that's having relations with his mother. I think it is sick and I have lost all respect for my mother. My kids (her grandkids) are dissapointed because they know too. Oh and yes if you are wondering he is still very married.