It is quite tough, my DH is a bit more horsey than yours from the sounds of things in that he quite likes them, has occasionally ridden himself and will help out with looking after them in an emergency but he's never quite been bitten by the bug or 'got' the lifestyle in the way a real horsey person would. I would say the key things are communication, forward planning and compromise. The last one is particularly important, it's all very well saying you've been clear but you need to listen to what your DH is saying and take that into account as well (and equally he shouldn't get to dictate to you either).
DH and I have always been incredibly strict about financial planning and fairness which I think is essential when one or both of you has an expensive hobby. We have regular budgeting conversations so we both fully understand our essential spends, agree an annual budget for shared 'non essential' expenses like eating out, takeaways, holidays, days out, children's expenses (when we had young DC), Christmas and birthdays - we don't always fully agree as if it was just down to me I'd cut back spending on those things to the bare minimum so as to have more left over, e.g. never or very rarely go on holiday (who wants to be away from the horses anyway?
) whereas for DH these things are really important so he'd spend more, so we have to land somewhere in the middle. We also agree what our long term financial goals are e.g. house renovations, retirement planning and allocate a monthly amount towards savings for these things (luckily we're very much aligned there, neither of us care about things like a big house or a flashy car and we both work in the public sector so excellent pensions). What's left over is our personal spends or hobby money, and this is strictly divided exactly 50:50, even at times in our lives where one of us was earning more than the other.
The net result is I haven't always had enough 'spare' money to live the horsey lifestyle I've wanted and I theoretically 'could' afford on our joint income, only in the last few years since the children have grown up and we've downsized our house have I been able to afford my own (before then had to make do with lessons and shares) and even then not exactly the horse I would have purchased or yard I would have been on or activities I would have been doing had I only had myself to consider (currently have an older Connie boy on full loan at a fairly scruffy/low key riding school based livery yard, in my dreams I have a string of high powered yet incredibly well mannered sports horses on full livery at a fancy competition yard and am out competing or hacking in beautiful countryside in my top of the range lorry every weekend
). But obviously much as I wish I could have both the dream lifestyle and my marriage intact, in the final analysis I would still choose being married to DH as I love him and all that 😘over singledom and being free to spend all my money on horses, I guess that's the choice you have to make in a marriage.
If I'm being honest I do sometimes get annoyed because DH doesn't spend his share of our 'spending' money on things in my heart I find 'worthy', I would understand if he had a different absorbing hobby he spent all his money and energy on like I do on the horses, but he's more of a potterer/fritterer, his spends go mainly on things like nice lunches and coffees when he's in the office, bits and pieces for his computer, having the latest/top of the range phone, computer games, music, food/drink subscription services, that sort of thing which in my less admirable/loving moments I add up and think how many lessons or saddles I could have bought with the money he's 'wasted', but then again he's seen me do things like spend thousands on vets bills and rehab livery for an irretrievably broken horse or spend £££ on lessons where I end up crying about how bad a rider I am or competitions where I've been eliminated at the first fence and similar, so he'd have a perfectly logical argument that I'm the one throwing money down the drain 😂 Over the years we have both learnt to keep such thoughts firmly unspoken as down that road marital harmony does not lie!
We have also had to discuss and come to compromises on how much time I spend on the horses which in a way is more difficult than the money, as I say DH does like his weekends away and holidays so I do have to have the ability to leave the horses sometimes, equally I have to really plan our weekends and put the energy in to e.g. getting up at the crack of dawn on a Saturday to feed/turnout or only ride for 20 mins rather than going on a lovely long hack because I know DH has planned a nice day out for us later, again worth it for the sake of our marriage even if I secretly sometimes would rather spend it with the horse!