Responses
If his mom cheated, I wouldn't be surprised if his dad barred all contact out of spite.
I agree about There's nothing wrong with her still wanting to be in her child life and wanting to get to know him. That's fine. I don't like that she didn't tell him that he has a sibling. He was just thinking that he was going on to see his mother and nobody else.
A lot of people seem to be badmouthing the mother, but I don't think she deserves all that criticism. First of all, while it was horrible that she cheated on her husband, let's not forget that the husband was also at fault for neglecting his family. Can you really blame her for wanting to find someone else that would appreciate her?
And she has all the good intention of wanting to connect to her son again. She tries to reach out because he is still her son and she still loves him. There's nothing wrong with still wanting to be in your children's lives.
Also, in a society where homosexuality is still being misunderstood and prejudiced against, her reaction would be quite reasonable. It's not a good reaction, but she doesn't really mean any harm. In fact, I would even argue that her reaction shows that, deep down, she still feels guilty for leaving the family.