Well, forget J for the moment - he's disappeared and may or may not reappear. I think that you and your husband need to mend the trust between you - you need to 100% come clean with him. Be honest about what happened, and how you feel. That may cause some upset, and you need to let that settle.
Then you may want to talk with him about what could happen is J ever shows up again - what sorts of things would he feel comfortable with, and what would be completely out of bounds. That may take a while, and lots of talking, but you should eventually reach a common understanding.
Then, if and when J ever shows up in your life again, you can go forward in the knowledge that you and your husband have made an agreement.
Now, as to what may be going on in J's head - that's a whole different story, but I don't think that is something you should be needing to worry about for now.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb