Time and Place
You sound like you have a pretty good head about what's actually going on. My sum up is:
If you are having a date night he should act accordingly. I have seen the best results come when each person gives their complete attention to the person they are with. The girl I'm dating currently (I) is fantastic at this. If she's with one of her other boyfriends, they are the center of the rotation of the planets, if she's with me, I am.
The tendency to be needy, jealous, and demanding is something we should constantly strive to move past. However, just because we are open does not mean that we don't have the desire to feel loved and special. New love is so powerful that everything else gets the volume turned down, including our other loves, that's just the way it is. However, he may need to practice on his focus - being *with* the person he is with. There will be plenty of time for cyber with his other girlfriend when the two of you are not having a date night.
The other side, if you are not getting what you need then you may consider taking it upon yourself to get it elsewhere. We all need to get a good thrashing on a regular basis, if he's not in a position to give that to you right now then perhaps you should find someone who is. That is one of the beautiful things about being poly, my partner doesn't have to meet all of my needs: they have to meet the needs they *want* to and I get the others satisfied someplace else.