Sounds like it could be a time management problem. You are tired of sharing your wife because your time/space management needs are not being met at home? You also don't want to date the GF. You do have her as your metamour.
Could tell her and wife direct --
" I would like to set an appointment time to talk about two things. In general...
1) We tried. Me and the GF do not work as a couple because I find I am monoamorous and my wife is IT for me. You and wife can keep seeing each other, but I am best off in the role of husband to her, and metamour to you. I am sorry the dating experiment came to this outcome but it is what it is. I would like to remain friendly. We could talk about all that more deeply -- changing from a triad back to V smoothly.
2) GF is over X times a week. I need some alone time here with wife. I need time alone with me. Could you both be willing to talk to me about space/calendar/time management issues so everyone can get what they need in terms of time and space? I feel crowded in my home. I need to be free of that feeling.
3) Do you have needs of your own that need addressing? When is a good time for all of us to talk so we remain in healthy relationship in our respective roles?"
Tell each separate and then together. So there's no triangulation and you get an appointment to talk in trio about these issues.
I was nursing for a long time - wife could take the nursing babe WITH HER to her GF's home. I took the nursling wherever I went. It is what it is in that stage of life. That is the price of admission wife could pay to a) keep harmony with you and b) still see the GF and C) meet the baby nursing needs all at once.
The "triad" configuration did not fly, but in a "V" you are still in polyship here. You do not want to divorce, but the polymath balance
need to be restored to meet your needs too. So speak up so you have be ok in polyship with your polyship people.
Each mini relationship inside the larger polyship needs to be in balance for the overall thing to feel ok and flying true. Right now you sound like you fly crooked because you had unarticulated needs were going unmet. I am glad you took the bull by the horns and have opened a dialogue.
Good for you!
You do not want a divorce. So could give it places to go where you could be ok --
Like she takes the nursling with her. And / or she leaves to see the GF after the kids are post bed/bath/story time.
You all make a calendar to address the polymath needs that are unbalanced right now:
- Time for you alone
- Time for you and the kids alone
- Time for wife and kids alone
- Time for you and wife alone
- Time for you and wife and the kids alone
- Time for wife and GF alone
- Time for you and wife and GF without kids
- Time for all together -- you and wife and GF and kids. (This is being overdone, but don't overcompensate and make it ZERO.)
Could take it on the semester approach. We do that here -- "Here's the map for THIS semester." Then people only have to suck up on compromises for that term, knowing that next term
things can readjust again to meet changing needs.
Sometimes knowing that helps -- "Alright, just for this term. Next term I can ask for different at the check in time."
Could ask wife and GF what THEIR suggested solutions could be for meeting all the people's needs. Then you all cobble something together from those puzzle pieces that could work and agree to try it for a time and see. Check back in to evaluate after X weeks to see if things are good or still need tweaks. Could hold each other accountable to agreements/promises made.
Hang in there!