@BillRM,
You state that "it was one night, I went out with him for 2-3 months, found out I was pregnant 2 months later".
Your son has a Father. You need to bring him into this World and on-going, happy, lively, teach him all the good things in life, to learn and grow and never go against the law. He'll thank you later. Your husband deserves the wife he married, the one that is interested in him, the one that took on your child and is raising him. You deserve peace it was one night in retrospect or a few weeks of dating.
Joe? Made his choices in life. He has to live with that. Send him photos every now and then, he deserves also to see his son grow but to me, that's the end of it. If he was out of jail fair enough. He's not. He's already had fights in there, you show your face or that of the child, who knows what stalker will stalk you to get back at him.
This is my opinion.
Most children that grow up with a "step-parent" in a happy environment love that person as if they were their own, somehow most have an inkling that they were adopted or that the parent was a step parent - you could always state you have 2 Daddies you'll meet the other one day, Mummy and Daddy love you very much.. Just a couple of times so that it's there in his mind and one day he'll ask you.
I do think for your marriage sake, for the child's sake, you should not even broach the idea at this point in time. You should concentrate on the love of 3 and bring this child up in a happy environment.