I think you are probably a little bit like me. I could be very happy as a mono in the right relationship, but a relationship with a poly is not that kind of relationship. Does that make sense?
I don't know if the link you got sent enabled you to find a good article on jealousy, I clicked on it and didn't. I think there is something if you go into www.xeromag.com
and look under the article titles.
What it seems to boil down to is partly that the jealousy is bringing up something that is lacking in your relationship, so you are triggered when someone else gets that something. In your case it could be quality time with your partner. With three kids that is hard to get at the best of times and then to have someone else eat into it must be doubly hard. I can see why you go and see others as well but in some ways that would be a double whammy if what you really want is quality time with your partner. That's one of the reasons I haven't yet seen anyone else, I feel like I'd be biting off my nose to spite my face.
I said "partly" because for me there is also the loneliness factor. My partner is my favourite person, I miss him when he's gone and when he's gone to be with his OSO I miss him more, imagining him in her arms.
I'm hoping to improve our situation by developing more of a triad with OSO. But somehow I don't think that will be the end of it. Z loves women. He has a 'type' and if she happens to be unhappy he wants to make it all better. Not that he acts on it but I can see it's there in the very framework of his psyche. I find that labels are helpful, If I hadn't labeled him I would still be without the support I've found in the poly community and trying to figure out this amazing but very unique partner of mine.