DH and I are building a house together, it's very stressful at times and your entire life revolves around it for the duration. The only reason we are coping and coming through sanity intact is because we were both in love with the project and are both equally motivated. I can't imagine going through it at sometime else's behest.
Unless this is a modest project, as in mostly cosmetic and you can go at it a bit at a time not biting off more than you can chew...
Then I think you need to pause, admit it was an error of judgement to dive right in and see if you can identify an exit strategy that you can make work.
The fact you pushed for this was naive but you didn't intentionally railroad him (I hope). It is very easy to underestimate what you're taking on if you don't do your homework and go into it with your eyes wide open.
Apologise, for the naiveté and uninformed enthusiasm.
Maybe you were selfish if you weren't listening to him and overrode him, but if that wasn't a calculated act, then it's the kind of thing you do when you've got tunnel vision and are making decisions too fast. So maybe if you can accept the part you've played in getting you in over your (joint) heads then maybe you can salvage something.
But if this is way more than he ever wanted or is able to cope with then it has essentially hijacked his life until he/you can get free from the situation.
I would put the brakes on work.
Get some decent advice on how all the options from selling now to slowly chipping away, to doing a minimum and seeking in 18 months would work... And work out your best plan.
The relationship will either survive or it won't, but an apology is a start.