Do i tell my son my husband isn’t his dad?

I am honestly at a loss of what i should do and have no one i can ask to get meaningful advice and answers.

I got pregnant the beginning of my senior year in high school and my son is now 12. The guy i was with was older and before i found out we broke up because he got caught up in things i wanted nowhere near. However when i found out i was pregnant he had went to jail. My son thinks my husband is his dad because thats all he has ever known. We got together when he was a little over 2 and have other children. No one knows but a few people the truth. Now to what i need help with. Do i try now to reach out to him or leave it be. Do i my son or not. Do i wait a few years till he understands. I just don’t know what to do. I did what was right at the time and now as my kid gets older i don’t want to do the wrong thing.