one sticky wicket to consider
The only thing I would say, not to be difficult, but as a very monogamous person currently in love with a poly person, is that it is almost impossible for me to consider falling in love with someone else while I am with him--because part of my monogamous nature is that I am not interested in anyone else. I've tried to be, to see if it would make the situation easier for me, but even people I know I'd be interested in if I was single don't appeal.
So, being with you might prevent him from being able to connect with someone who can give him what he wants. This is not meant to be a criticism of you, or to imply that he can't make his own choices, or that your relationship could satisfy his needs long-term...
It's just a truth for many monogamous people that might not occur to poly people, who are naturally able to find other, new people attractive while being in love with someone else.