Here's what I get from it. I could be wrong.
- He (my metamour) spends the majority of his time maintaining that (other) relationship.
- My partner (our hinge) is struggling with his lies and him not being available for her.
- I'm trying to be supportive of her and this relationship because they have so much history together. I grow tired of it.
- Could I continue to be supportive? Or do something else?
Sure. You could do something else if what you currently do is not serving you.
- Your partner could be going through stages of grief and not at final acceptance. Perhaps this relationship is fizzling. You could talk to her about that and ask her what she needs at this time. Then decide if you are willing/able to provide that at this time or not.
- You could tell you partner that the bleed over is too overwhelming and you need a break. So you encourage her to talk to OTHER people about it so it's not all you. You are willing to listen to some, but the load is too big for just you and her to hold it -- could encourage her to vent elsewhere also.
- You could talk to your metamour and ask if he's willing to stop the upsetting behavior (lies).
- You could do nothing and let time pass and see if new info or new actions occur on their own.
- You could stop being supportive of this relationship.
- You could do something else I cannot think of right now.
- You could mix and match options above.
Which is not so bad but he rarely has to clean up his own mess.
This seems like you resent his behavior and/or blame him for the wacky. While this may be so... could there be any behaviors your hinge is doing that you resent or grow tired of?
What are YOUR needs here? For harmony and this to stop? Something else?