It's a small wall of text that still doesn't cover much, but hopefully you'll find some of that advice/story useful.

There are a few good books around on the topic of polyamory, like Ethical_Slut.
In my opinion, essentially it's challenging, yet difficult, because, well because it's poly. There is not one model to follow. I think quite a bit of it has already been somewhat accurately

Personally I fall into that top open-relationship/poly amory area: "This is my wife, my girlfriend, my wife's boyfriend"

It seems that right now you're surrounded by conservative-minded people and have only one confident with whom you live, so at least you have that safe space. Also, when you say you "*almost* had sex on numerous occasions" with him and you "really, really like" him, it sounds to me that you have some partner choices to make. I'd encourage you to be upfront about it to your partners, and simply dump the ones who would obviously not be able to deal with it (though feel truly free to disregard my 2 cents advice.)

Anyway, being honest and dealing with jealousy are easier said than done. When I came out to my spouse a few years ago, she freaked out. Then we talked about it for several months. Despite feeling really jealous, she agreed to try to open our relationship and allowed me to make out with other people. We talked some more (a lot more) and she saw I wasn't going anywhere and that it hadn't made our relationship weaker. We kept talking and redefining boundaries and talking and so on. Now we both date, individually, a small number (1-2) or people outside our marriage. We also wrote a relationship agreement with what is ok and what is not (from "how far you can go on date X" to "Wash the sheets before the spouse comes back" to "Accepted behaviors when in public with someone else"). So, that's my model, for now.

I guess you could figure out what relationship configuration is best for you and aim for it, while in the meantime compromising by settling for less-than-ideal relationship. Or you could just be open about it to trusted people and potential dates and let things fall into place. I live in a liberal area, which makes it easier for me to be rather open and accepted about it, so I think location is also something to consider.