I think its completely unfair for him to ask you end your commitments to others simply because he is in crisis over your new relationship identity as poly, however, its important I think, to do some work together and spend some quality time with him. After all, he is in crisis. I see no reason why you can't say to him, "honey, I'm sorry you are having a hard time figuring stuff out for your self, let's spend the night talking it out and figuring out how you can go about getting your needs met and figuring out what is going on." Then I would let him know kindly and firmly that you will not be changing what you are doing to suit him but you will make yourself available to talk to.
There is no reason why he has to look for and be active in relationships out side of your partnership; nor is there reason to stick with men, to get about finding a partner right now or act poly ever again. Its all what you make it. Maybe this guy wasn't what he thought he was, maybe his hormones and beer got the better of him that night and now he feels differently, maybe it was enough to know he is a poly theorist and not poly in action. Who knows. Bottom line there is nothing to be concerned about, just to wonder about and to adjust accordingly.
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