I am a little confused as to why it's okay for M to date people you don't know, but not your friends. While yes, there are a bajillion people in the world, we usually make friends by meeting other people's friends.
Secondly, this is poly. If H dates J, there is no reason M can't date her too. It's not like the two are mutually exclusive.
That said, if you are accurately presenting the way M justifies his behavior, it sounds like sex is a sport. Not judging, but I can't relate to it, and would not want to be involved due to the incompatibility. That said, you do love him, so you can try to change who he is, which will likely cause you both misery, or state your boundaries and adhere to them yourself. Do not be hurt and offended if he does not adhere to YOUR boundaries; just extricate yourself on the grounds that your priorities are not compatible.