but it's not very easy to get to know him because my partner doesn't trust us around each other, and doesn't want to see him get hurt by my hurt.
Is this an open, honest polyship she's trying to build? Could ask her.
If so, what's the fear here that the two metamours will compare notes and find out what
exactly? Why does she not trust you guys alone? Could ask if she's willing to explain that.
And she doesn't want to see him hurt by your hurting.... So she does indeed recognize that you ARE hurting... but that
doesn't bother her to see?
Could ask her on that point too.
You could ask her if she's willing to read about jealousy
and more jealousy
with you. And how to avoid pitfalls
and poly hell
with you and be supportive in your process even as she enjoys her new relationship. If she wants to be a hinge, she could tend to ALL her partners. Maybe other articles
could help you both navigate this space. I'm sure other people could give you other links.
If this polyship is too wonky for you, you could decline to participate in it and tell her you are not up for it like this.
You are responsible for your own well being and what you choose to participate in.