Okay, so I just checked out this pdf entitled "Making Peace with Jealousy in a Polyamorous Relationship," and I don't think it really applies for us. I'm not saying that it's full of bad advice, but the premise is kind of off. I'm hoping you have an alternate resource that doesn't automatically assume that the participants are 100% on board with polyamory, which I of course am not. I'm monogamous.
Essentially, the document assumes that I'm overwhelmed with fear that someone will steal my sandwich, so to speak, and the thing is that I've already declared that the sandwich isn't up for grabs - and I am not afraid that someone will be able to steal it from me. In this case the sandwich is my exclusivity, and the fact is that I will either have a level of exclusivity that I'm comfortable with or I will end the marriage. It's really not that complicated.
So ... what exactly am I supposed to be afraid of? I'm not upset that my husband is in love with someone else - I'm upset that he's lied to me and damaged our relationship over the past six months. I'm not worried that Sarah is "better" than me in some way, or that John will leave me for her. I'm not afraid that at this point I can't trust him anymore - if I felt that way I'd be divorced already. I don't think being monogamous automatically means you are jealous, and I don't think monogamy is wrong or a sign of weakness. It just is what it is.
The one thing I am afraid of is the resentment that every polyamory resource I've seen so far says is only natural for my partner to feel in his position. That's exactly what I said above will probably happen regardless of what path we take (Sarah and John still being in each others lives, or not), because there is no path forward where they get to have a fully fledged polyamorous relationship. It's the very resentment that I've been experiencing for months now. So maybe at this point it doesn't even qualify as a fear, because it's already happened. It's a reality.
So do you have anything that will help deal with our main problem - the resentment? Something that can help prevent the relationships we have from continuing to be damaged by that resentment?