I just wanted to welcome you to our forum.
I suspect that the key with J is to take any relationship form at a slow pace, and include a lot of communicating. He has to know what your concerns are, not just that you're poly and (?) "available."
You've traveled a long journey to get here; I feel confident you will exercise due caution and do research along each step of the way. I hope Polyamory.com is of good help to you, and you'll probably be of help to others as well.
Glad you could be here.
Love means never having to say, "Put down that meat cleaver!"