I just want to clarify for everyone that I completely trust my fiancee. It's more I'm suspicious of the guy's intentions in some irrational part of my brain, despite realizing that it's probably on the up and up. Hence, "I hate feeling jealous."

Bottom line is you either trust your fiancee or you don't. No trust, not a good foundation for a relationship.

Ooh
To trust is to give the benefit of the doubt.
If you have concrete evidence then there’s your answer.
But don’t make assumptions. If the kids are good friends she will want to check out the parents.
Also for all you know they could be discussing you and how much she loves you. 🤷🏻‍♀️
I just think you shouldn’t jump to conclusions.
If she had something to hide she wouldn’t be telling you anything.
It sounds like she maybe guilty of trying to make you feel jealous and if that is the case that’s a whole different issue.
Just talk to her.
But do not accuse her though. Which I’m sure you already know all of this so apologies for my directness. If that’s a word? 🤷🏻‍♀️

Not a great way to start, no trust 🤔

Let go of your needless jealousy.