Most Helpful Guy
I'm in a polyamorous relationship, and I generally encourage partners to 'get out there' a little bit, as it's kind of the only way to handle the time management. It does sound like he is drifting into some jealousy issues.
You may want to talk to him about it. The only way poly can really work is if things are all out and open and discussed. It is a lot of work emotionally, and there are clearly some issues that are not being communicated. If they continue without being addressed they will short-circuit the relationship. The 'joking' comments sounds passive-aggressive, and the open nature of the relationship won't work if you feel emotionally punished for pursuing something. That's not how it works.
Most Helpful Girl
Is he your ex or your bf?