should I tell my sons dad I gave him up for adoption 10 years after?

[Beautiful]

Ten years ago I was in a short relationship with a man. I left when I saw I couldn't trust him alone with my 5 year old daughter. He would lie about things she had done while i was gone or say I needed to beat her for little stupid things. Like she lost his cup of pens somewhere... We found it in the closet where she and I had built a fort.
Any way, after I left I found out I was pregnant. Oh God. I couldn't let him raise this baby, he was abusive and liked to drink. immature and selfish. He was down right scary some times. I was 20 and he was 26.
I gave the baby up for adoption, the hardest thing I have ever done we stay in touch by letters and pictures every Christmas.
Well his dad just found me on Facebook and I found out he's a different person. He attends his other childrens school functions, (children had nothing to do with previously) volunteers at his church and is a drug counselor! Do I tell him? Or wait till he's 18 in case he tries to disrupt his life
I'm lost.