Definitely a bit different, but my wife and I realized we were poly by first having 3somes. At the start there were ALL sorts of rules that she had. As time passed and she saw that I was respecting those rules, she started removing a few. By talking and sorting through our feelings, TOGETHER, we came to learn that we were indeed poly and started exploring this lifestyle. Before you know it, all rules were gone and we were able to invite our first gf to move in with us!!
This is gonna take time and a lot of work on everyone's part. I don't think rules are bad, so long as you explain why you have them and he agrees. Also remember that he may not "like" the rules, and that's ok, but he should respect them. Just like any relationship, there's a lot of compromise that needs to happen.
Hope this helps some.