I'm sorry you struggle. Let me repeat back what I understand in my own words. You correct me if I get it wrong, okay? I've put it in blue just to block it off.
You are participating in a poly V with Isabelle (hinge) and Leo (your meta.) In other words, Isabelle is dating the both of you.
You and Leo have talked. Leo confided that he doesn't really want to be doing a poly V. He'd rather participate in a monogamous thing. But he is doing this because he’s afraid that if he tells Isabelle how he really feels she’ll leave him.
Isabelle doesn't know Leo feels this way, or she knows, but isn't doing anything about it.
You hate being put in the middle like this. You think it's an unhealthy dynamic. You also don't want to break up with Isabelle.
Is that about it? If so, then, in your shoes, I think I would do this: Tell Leo you are sorry he's struggling, but it really wasn't fair to tell you about it. You cannot be an impartial ear, because you are one of the people INSIDE the poly system. In future, you'd prefer he talk to Isabelle directly about problems with Isabelle, or air it out with people OUTSIDE the system, like a counselor or other friends, to get his thoughts in order before talking to her. Don't tell you, because you are not a "regular friend." You are his metamour and INSIDE the system.
Now that Leo has told you this stuff, and made it your business, does he plan to inform Isabelle, or not?
You set a time limit. You could tell Leo you encourage him to talk to Isabelle directly within the next 2 weeks, or else you will tell her yourself. You can hold his secret for that long, no longer. Leo either does or does not deal with his business. If he wants all three of you to talk, you'd be up for that option too. But this can't drag out. It's not fair to ask you to keep secrets that are hurting someone (Leo himself) or could hurt someone else (Isabelle). You are also hurting now with this knowledge.
Depending on how Leo responds...
A) You wait. Hopefully Leo takes personal responsibility and talks to her within the timeframe.
B) After waiting 2 weeks, or if Leo chooses this, you and Leo ask Isabelle for a time to talk all together. When the appointment comes, you give him a chance to talk first. And if he still doesn't, or wimps out, you lay it on the table. Leo told you that he doesn't really want to be doing poly, but is putting up with it because he's afraid Isabelle will dump him. He overshared with you, and you feel uncomfortable participating in this poly V, now that you know Leo may be doing things he doesn't really want -- like he's doing poly under duress. You and Leo wanted to talk to Isabelle and sort all this out.
C) After waiting 2 weeks, if there is no movement from Leo, you just tell Isabelle. Leo told you he doesn't really want to be doing polyamory, but isn't telling Isabelle because he's scared she will dump him. Instead, he told you. For what purpose? You don't know. But now YOU are uncomfortable participating here, if he's basically doing stuff he really doesn't want to be doing. You told Leo this made you uncomfortable and that you'd prefer he talked to Isabelle directly, and gave him 2 weeks to own it and do it. But he hasn't, and you don't want to drag things out. So now you are informing her.
D) You bow out. Isabelle does nothing/already knew/is okay with Leo doing poly under duress and harming himself. You are not okay participating like that. So even though you don't want to, you break up with Isabelle because you do not feel like doing wonky poly. You prefer it is on the level, with all parties consenting.
There might be other options, but those are all the ones I can see.
Even if other people want to be doing wonky stuff, YOU don't have to.
But yeah. Being put in this position-- it just stinks. I'm sorry this is happening.
Sigh.
Galagirl
