I got a letter from my son

It's been really hard.. I signed my rights away ti my 16 year old... He wanted to be adopted by his foster mom and I had already been gone for years and he cried in court begging them not to send him with me.. It hurt knowing that being back with me caused him so much pain ... So I put him first and signed my rights away so he could be happy. I told him I would never bother him again and I just want him to be happy. He was hugging his foster mom(mom now) and didn't say anything to me... I got a letter in the mail a couple days ago and it was from him. I didn't know what to say expect. I waited a few hours to read it and curiosity finally got the better of me and I open it... I read it 3x. The gist of it was he was thinking me for allowing him to go home with his mom, but he said it doesn't change anything and that this won't take back all I put him through. He wishes me the best but he's emotionally killing me off and is just gonna treat me like I'm dead, but he wanted to say something to be before he did that. He said he hopes I'm able to find happiness and peace because he has thx to his mom. He said this will be the last thing I hear from here and he again wishes me the best (called me by my first name)... And that was it...