Welcome to our forum.
My basic impression is that you are handling the difficult situation as best as possible. Make sure you don't try to "gobble up the whole elephant at once;" take things one small bite at a time.
It sounds like this is a very emotional time for your husband? I got the impression maybe he had "developed a short fuse." It is big of him to give you the okay for seeking sex outside the marriage, even if he did so reluctantly. He was very fair about it.
Is he seeing a therapist at all? Are the two of you in couple's counseling? (preferably with a poly-friendly therapist.) Perhaps there is something that is holding him back emotionally (where intimacy is concerned).
I think SourGirl made a good point in that some of his concerns/worries will have to be addressed by seeing, through experience, that you aren't going to leave him. Just offer what reassurance you can, while letting him work through some of his emotional turmoil. "Trying to 'shush' someone's fears can be very frustrating to the person that feels them," as SourGirl said. This doesn't mean you ignore his fears, it just means that you acknowledge them, offer him some reassurance, and then let him work through those fears.
I hope Polyamory.com has been of some help to you so far, and will continue to be of help.
Love means never having to say, "Put down that meat cleaver!"