I think I said in that other thread (or somewhere on this forum)...
When I was seeing Guy, he and Hubby were friends by some loose definition. Hubby and I met Guy the same night at a party, and they had a brief discussion about me that led to a mutual respect. They didn't talk to each other often, but if you'd asked either of them, they would have said they were friends. (Obviously the friendship ended when Guy's and my relationship did, because of the nature of *how* it ended...)
I asked Hubby and S2 if they would be willing to meet each other, but made it clear that I don't expect them to be friends, and that if they weren't okay with meeting, I would live with it. For me, that was more of a comfort thing. I wanted each of them to know who the other important guy in my life was, to at least have a mental image of each other and open a line of communication if needed. For example, I have health issues; if I were to be hospitalized, I would want Hubby to let S2 know, which would be weird if they were total strangers up to that point.
They agreed to meet, and seemed to hit it off well, but neither has any interest in befriending the other. They're more comfortable knowing who each other is and seeing that each other is okay with the whole situation, and that was all they wanted. And I'm okay with that; I actually prefer having some distance between them. It makes it easier for me to be with Hubby when I'm with Hubby, and with S2 when I'm with S2; I like being the hinge.
Right now, they're both exclusive with me. If either of them became involved with someone else, either sexually or full relationship, I would want to meet her for the same reason I wanted the guys to meet. But I would definitely NOT want to befriend her, because that would feel awkward as hell to me, and because I am prone to jealousy and so wouldn't want to spend too much time with any metamour. I own my jealousy, but to minimize it and minimize the risk of me saying something inappropriate, I'd rather keep a distance.
Holidays are way too complicated as it is, so I don't foresee any gatherings that would include all of us. Hubby's family is big on Thanksgiving and Christmas dinners and expect us to show up, with or without my kids, for at least one of the two. My mother is mortally offended if we don't show up at her place on Christmas *with* my kids. Alt and Country end up having at least 2 Thanksgivings and 5 Christmases as it is, because their dad's family has huge get-togethers; their stepmother's parents are divorced and each of them expects to see the kids with their dad and stepmom; and then they have Christmas (usually before the actual day) with us with Hubby's family, and we go to my parents' for a few hours on Christmas Day.
So that's more than enough scheduling nightmare. If we threw S2 into the mix, we would have to work around him having Spikes and Beads, and him going to his huge family's dinners. (He's the youngest of 6, and each of his siblings has at least 2 kids...from what he's said, it gets loud, crowded, and you MUST BE THERE if you're part of the family.) For this year at least, given that S2 and I have only been seeing each other since July and his family and Hubby's don't know the situation, holiday get-togethers are out of the question.