Normally I never would, and I will advise people against it every time. 9/10 times it is a very poor idea. BUT I do co-own a mare with my ex boyfriend. It works out just fine. Long story short, we were together 6 years, common law, but always better off as friends. His family had been into horses when he was younger, I wanted to lease said mare - he bought said mare instead. We've remained good friends and he is at the barn every day to clean her stall/groom her/ride her and everything else that goes along with ownership. I ride the mare as well, she's my hunter horse and I could never afford a horse like her on my own, but we simply do not have the bond that ex-boyfriend and her do. My other mare is my heart horse, and I do love this mare and will never part with her, but ex boyfriend and her are like two peas in a pod so he stays co-owner.