FWIW, here's my opinion.
Your greatest want seems to be freedom to date whoever you wish. Well... keep following that track. Don't be changing horses midstream -- that adds to your confusion.
- Get you into your own apartment.
- I can see buying the smaller house with wife so that finances become easier on all and child is solidly provided for. (If you live in the MIL apartment, do so only for a year.)
- Next up would be sorting our divorce paperwork. Provide for your ex and child and make coparenting schedule and all that.
- After that? Sort out if you and soon to be ex-wife want to still date as a non-married couple in a polyship.
- After that is sorted out? THEN see if you want to help GF buy a house and in what fashion. Gifting someone money -- talk to your banker about how to do it right so it doesn't ding you later and all the taxes are sorted out.
I suggest that order, and taking a few years to get though it. Get the old stuff done before tackling a new bullet point. Not trying to be doing it all at the same time!
You living in the MIL apartment on property for a year as the dust settles on that stuff might not be too bad. That's kinda like moving back in with wife and child, but not so close you go back to being unhappy as the adults sort out their business. And the child isn't experiencing SO much change at once. Slow the process down for the kid as well as the adults.
But if you can afford to live in an apartment and just rent out the MIL apartment on the new property -- could do it now rather than wait. That's a lot "cleaner." End up in your own space for the next year though -- however you do it.
FINISH sorting divorce things. And how dating wife or not afterward fits into that picture. At that point, wife would be in small house, you in your apartment (wherever it is) , and GF at her place.
Slow all this down, so you can finish sorting out what it is your really want from life while still attending to your responsibilities. Wife and GF have time and space to sort out what they want from their lives and if that includes still wanting to be in polyship with you under new circumstances.
If they get too "tug-o-war" with you, you have a place to retreat from BOTH. Right now you do not have that. There is the freedom TO date who you want that you are aware of. I wonder if you also want freedom FROM too much pressure?
Take a year. Do NOT rush to live with GF permanently. Overnights, fine. But slow down the GF entanglements. Thank her for the kindness in holding you during separation crisis for a few months, but seek to stand on your own before you try that living together with GF again. I think she took living together as a bigger thing than it was -- like some kind of increasing commitment to you.
Helping GF buy a house at this point in time? New business sounds premature when you have other business still left unsorted. It sounds like a potential mess and rushing in too fast.
It great that she wants a house, but if she wants it right now? She could get it on her own WITHOUT your help. If that means she has to wait and stick with her current place while saving some more for her downpayment -- it is what it is.
You are experiencing MANY major life changes at ones. The
Holmes stress scale might be something you want to look at.
I could be wrong, but I am seeing at least
marriage separation (65)
divorce (73)
taking on new mortgage -- wife (31)
change in financial state (38)
change in residence (20)
change in health/behavior of family member (GF upset -- 44)
reconciliation -- if you and wife decide to divorce but keep dating (45)
taking on new mortgage -- GF (31)
which clocks in at 347. Which suggests 80% chance of major health breakdown in next 2 years.
If you only do the blue stuff right now, and deal with the rest slower? It's 207. Still high, but changes to 50% chance of health break down.
I
strongly suggest you find a way to slow things down and not pile up all these happenings at once. Finish the old business first, before starting new business. And consider a therapist for extra support in this challenging time.
We are going through the Jealousy Workbook page by page together, and she's open to being poly, but I just don't think she's open to me being poly with my ex.
If that is your GF's bottom line? And it doesn't match what you want from your life because you DO want to explore things with your ex? Then you could break up with her and not be dragging it out or creating new entanglements with GF. Seek to reduce your stress -- not ADD to it.
Again, your greatest want seems to be freedom to date whoever you wish at this point in time. If GF wants more commitment than you can give right now, be honest and up front with her.
Galagirl