Welcome to our forum.
I don't have a lot of advice for you sadly, other than to "refer you to some other sources." It sounds to me like the three of you are doing the best you can, figuring things out as you go (which is what we all must do), and like you and S *do*
know what rational communication looks like, you just find that your emotions get the best of you at first. Said emotions may do gradually less of that over time, just with patience and practice.
Re: jealousy ... haha SouthernGal, I'm so gonna one-up ya on this one. Bet you're jealous!
Let us discuss the greeneye monster shall we?
How to slay the greeneyed beastie.
Jealousy, Envy, Insecurity, Etc.
How do you achieve compersion?
The Theory of Jealousy Management
The Practice of Jealousy Management
Jealousy and the Poly Family
Brené Brown: the Power of Vulnerability
Yes, and there's your bonus list of all-about-jealousy links. (When I'm good, I'm good. As they say on Little Nicky, "Good luck with your nipple rubbing!" and, "Oh I don't need luck. I'm good ..."
Right. And as for links on how to navigate your poly life and relationships in general? Well I've got some tasty bites for that too:
Golden Nuggets board
Book and Website Recommendations
" by Tristan Taormino (book and website with cool resources)
Franklin Veaux's poly pages
And of course there's lots more good material out there (both on this site and on other sites), but the above four links should give you a good place to start.
Poly relationships tend to be stormy in the early years, so don't panic if you run into some heavy weather now and then. Just keep reading and learning and posting and ... oh! That reminds me: Check out all kinds of threads and boards right here on Polyamory.com; see what calls to you; share your thoughts and ask us any questions you desire. That, too, will help give you ideas of how to get your own poly sea legs.
Which sea legs will be quite unique amongst all other poly sea legs. Every person is unique; every relationship is unique. So what works for someone else may or may not be what works for you. You'll still have to do lots of that trial-and-error stuff, even after all the academic research you can do.
Hope your stay on Polyamory.com will prove beneficial!