I’ve been married for 15 years with my wife and our son is 18yo. I think I was a good father to him, always present, always supporting him, I was the first he talked to when he had a bullying problem, a math problem, when he needed romantic advice. He is straight but likes crossdressing and doing makeup, and I was the first one to support him on that too, while his mom was trying to make him more “masculine”.

However, recently I discovered that he is not actually my child. My MIL said he had to tell me something important, so I went to meet her and told me that my child is actually my wife’s high school boyfriend baby. She gave birth at 20 but apparently she was cheating on me with her old boyfriend. My MIL said my wife told her the truth after he was born because she had suspected that the baby didn’t exactly look like me and MIL confronted her about it, but the baby was already born and nothing could be done.?

I was mad and asked her why is she telling me this right not? She told me it’s because she saw my son hanging out with his biodad at a park and believes that he is back in their lives.

I decided not to shoot the messenger and went out to confront my wife and son about this, after a long argument they told the truth. The biodad was back and wanted to meet his real son.

A lot of shit happened and I’m divorcing, and also cutting my wife’s son out of my will, because, I never had a real son and all this time I was putting all my energy and effort raising another man’s child. I’m also consulting if is possible to sue the biodad for all the money I’ve spent raising his bio son thought out the years.?

My wife is obviously mad at me, but my (step?) son is just devastated, I can see him depressed, not talking to me, and constantly apologizing. My plan was to divorce and cut contact with them right after that, but now I’m wondering if I’m going too far by punishing him too.

Edit: Everybody is asking this: The kid knew about his biodad for about 4 months before I discovered it. And yes, we did a DNA test, he insisted a lot of it and after it came back negative is when I think his depression really hit. Y'all right, maybe it is useless to sue the biodad, but I'll ask a lawyer anyway.

Edit 2: Many people are comparing my situation to being a step dad or an adoption. There is a difference, I thought for over 18 years that he was my real son. I 100% believe that adoptive parents are real parents and their adopted children are their real children, but they willingly went into the adoption process, they know their family is not blood family. I was tricked into my situation. If I had known my wife after the baby was born I wouldn't have cared because I knew it was somebody else's son, but I thought this was my real son and just now I find out that he isn't. Anyway, I need to talk to him when he feels like it.