(((Khenry))) - you are NOT an idiot. Most of us have done the same thing, over and over, until something in us just says "enough...I can't do this any more". You saw him, and you saw how he's still messing with your mind. He says your single, then kisses you like he's still your man. That's manipulation, sweetie, and he sounds like a pro at it.
Let him go off to his 3/4 house, and you focus on you and your son. Don't beat yourself up because you went to see him. We often NEED to see that the "addict behavior" is still there, despite him being clean, to get it to sink into our heads.
FWIW, my niece's mom didn't put my niece's dad on the birth certificate, either. She is VERY proud to have her mama's last name, considering what her "dad" has been like.
Hugs and prayers,
Amy