You ask good questions about whether H is allowed to date friends, but M isn't, and if H himself is offended by M's hitting on J.
J and I had a single conversation about 4 years ago. She was the wife of a friend of H's. We seemed to get on well, and I really liked her, but then she disappeared until recently. When H and I saw J and her husband at a club we frequent, we rekindled the friendship. But it was only when she and H decided that they might enjoy seeing each other that she and I made an effort to connect more. I really like her. So, she became a friend to me when she and H started circling each other. I'm not sure if I'd feel weird or not if H wanted to get involved with one of my friends. I really only have a very few people I consider good friends (ironically, my best friend, and M2!) So maybe I shouldn't worry about him hitting on my friends, because I don't have any more to introduce him to!
As to whether H is offended, he is, a bit. Because they hadn't really done any serious dating yet, he's still not completely invested in the relationship. But he did think it was kind of a dick maneuver.
M and I had a Come To Jesus talk tonight, and I think that the main outcome of that, at least for me, is that I need to grow a backbone and stand up for myself a bit better. It seemed to impress him, actually, when I said some of the things I did.
Ugh--whatever. I very much want to give this relationship another chance, foolish as that might be.
Me: married to H for 14 years.
M: Boyfriend of about 1 year.
M2: Boyfriend's girlfriend of about 5 years, and a good friend of mine.