So it sounds like both want to have the conversation with the GF in a constructive way. Could do it with a counselor. However you feel it is most useful.
The goals to achieve seem to be --
- he breaks up with GF so (she is his metamour only) and NOT (his GF AND meta.)
- He remains married to wife.
- He learns to speak up and meet his wants, needs and limits himself. (No mind reader expectations)
- His polyship partners respect his wants, needs, and limits once shared if reasonable (And wanting time to himself in his home with his spouse is reasonable.)
- He lets go of resentments.
- Wife learns to speak up when she notices things are "off" with her partner rather than ignoring.
- Wife learns to ASK for wants, needs, and limits updates if they are not disclosed.
- GF learns of limits/boundaries and respects them
There could be more things -- y'all list them out.
To me it sounds like you could write out your personal standard in this polyship and get the expectations, responsibilities and rights laid out. Address behavior done/not done and hold each other accountable better. It is ok to make mistakes -- people are not perfect. But HOW do you want to move it forward? With a spirit of what?
Compassion and forgiveness?
Resentment and grr?
Yes, you will all feel things. But feelings are not always logical and in the heat of the moment one can be tempted to do all sorts of stuff in behavior that is led by illogical feelings. Keep it on the stuff done/not done. The actions, the behaviors.
Can't be all "head" all the time logic.
Can't be all "heart" all the time emotion.
Best decisions are made head and heart together.
So figure out how to move this forward.
Could apologize to her for not being more clear in the past on wants, needs, and limits. Ask her how she would like to be treated from now on in a "V shape" thing now that the "triad shape" thing is not a runner if a "V" shape thing is the new plan.
DH can wish it was a two person thing but it is just NOT that any more. Could digest that and then focus on what you have rather than what you do not have.
Could focus on how you want to be together NOW as you break down the elephant
sized problem into smaller more manageable bits.
Hang in there.