You made you choice knowing that he might break up with you. But you wanted a child before you were too old, so you took the risk. Too bad he was not a really good man. He sounds very weak- complaining about his wife and then having affairs and staying with her because his family would ostracize him if he left her. I’m not sure you would have enjoyed raising a child with him anyway.
Good luck. I hope your son brings you every possible joy!