AITAH for giving my 18 year old an ultimatum

Me and my husband have 3 kids together. They're 18, 16, and 8. 13 years ago my husband had an affair with a woman who was in the military. She was also married. He got her pregnant and broke my heart. I told him the only way I would stay with him if he doesn't have any involvement with that woman or his bastard. He had a choice. Lose his bastard or lose his whole family. So he chose the latter and I told the mistress that if she ever spoke to my husband again I'll out her in the military for having an affair and get her dishonorably discharged.

she reached out 3 months ago to my husband all these years later and to tell me she told HER son who is 12 now the truth and he wants to meet my husband. I told my husband no and he respected that. My husband ended up getting drunk and confessing everything to my 18 year old and BEHIND OUR BACK our 18 year old son reached out to my husband's baby mama and spoke to her because he "wanted to meet his brother". My son always talked about wanting a brother but I stopped after two girls. He has been meeting my husband's bastard behind our back and I found out going through his phone because he was leaving a lot. I cried and told him I was heartbroken and he said he's his brother and my daughters brother. I said he's not. He said he is and he is a great kid and they've gotten close and the kid needs a big brother. That made me mad. I said he's not family. Their dad wants nothing to do with him. That was part of the deal and I gave my son an ultimatum. He cuts all contact or he can move out. He chose to move in with his best friend. I feel betrayed. He picked a "brother" that he's known for barely 3 months over his whole family. I told my oldest daughter I don't want her talking to her brother. I blocked my son. So much of these seems harsh but he broke my heart. He chose a bastard that he didn't know existed a majority of his life over us. I carried him for 9 months. I have the ultimate sacrifice and he chooses that over me.