Hi Lila. No doubt you have received some sound support and advice from the lovely people here, I thought I might chime in after having skimmed some of the details.
I think if I were in your situation I might have a need to put my foot down. he might be all elated (NRE) about poly now that he has a small inkling of what it is, but that doesn't mean a free card to go do what he wants. It sounds like he has a lot of educating to do for himself as do you. Its not a matter of jumping in if one wants to succeed. If it were I doubt this forum would be here!
I think I would make some firm boundaries about what you expect and would appreciate him to do. The first being to hold off for at least a year on acting out his new feelings, second would be to go plan date nights again and get into the habit of spending time together, thinking about one another in terms of romance and togetherness (don't talk about kids and don't do "dates" with kids) and lastly start researching (start by reading threads here and doing tag searches), talking about feelings, learning the words to use to communicate about this stuff, get involved with your local community, and establish a foundation.
He has a long way to go as do you on understanding where poly theory ends and successful relationships with others begin.
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