Thinking a bit more about this op, I think the issue with the horse and your time is a bit of a distraction.
Say for a moment that you had no horse, the lack of financial fairness and him not pitching in with housework would still be an issue presumably?
This has obviously been going on for a while if he was not great when your daughter was small.
So how did you arrive at the point where although he is the bigger wage earner, he contributes less, if I have that right? Why are you paying the mortgage alone? Why do you not have a pooled joint account at least for the household?
One solution could be for your dh to pay for a cleaner? Would he be open to that?
Are there any other horse husbands down at your yard on a Saturday who your dh could join to go out for a beer?
Could you get your dh involved in carrying feed bags, soaking hay, fencing repairs etc if he is in a trade?
Could you make it a tradition that he picks you and your daughter up from your yard on a Saturday when it gets dark and you all go out together?
A lot of husbands working in a trade would be glad of down time in which to relax and a quiet house and would be happy that their wife and dd were off doing something that they enjoy.
You don’t have to answer this but how is your sex life? Is that what he is really complaining about?
I wouldn’t necessarily assume that you would be able to afford the horse if you split though op. You might have to pay for extra childcare if you work shifts and two houses are much more expensive than one.
I agree with PPS that you might have to make some compromises with your dh such as go to the yard less frequently during the week? If you are on full DIY could you go to half?
But equally it’s such a shame that a grown man resents a horse and that you and your dd have found a hobby that brings you both such happiness. Did you discuss with him how much time a horse takes before you became an owner?
Does your dh know that we are only lonely when we rely on others to fill our cup for us! Why doesn’t he get a hobby and some friends of his own?
Again, even if you didn’t have a horse, It’s not your responsibility op to fill your husband’s leisure time for him.
Can you explain that this is a phase of time when you need to be down at the yard so much but once your dd is in her middle to late teens, you won’t have to be there with her quite so much?
Full disclaimer: I am a horse owner so my opinion may be biased. 😀