(he admits he’s a dreamy idealist with his head in the clouds!)
So....what does he intend to do about that as it relates to his interest in polyamory?? From my experience, one had better be well grounded before stepping into the polyamory "arena". Juggling multiple schedules, relationships, needs, etc., doesn't just happen on its own because it "sounds wonderful". It takes effort and work.
From what you've shared, I don't see where your husband is someone who wants to put much effort or work into creating what HE wants in HIS life. (Of course, we are only hearing one side. But, he has a job he hates...so what's he doing to make a job/career change? Has problems in his relationship with you....but won't see a counselor.)
I don't know the circumstances of your husband ending up in a divorced family with no father figure. But, people can get divorced and BOTH can still actively parent their children IF if they choose to make the extra effort that's required when they no longer have the convenience of being in the same physical household.