Glad you were able to extricate yourself from an unhappy situation; it sounds like he was playing the both of you to make some extra cash.
I’ve had a lot of inquiries about sharing the lease of my mare between two people on those occasions that I put up a “for lease” ad and I never agree to it, for reasons which you have mentioned in your own experience. Too many opportunities for “he said/she said” and passing the blame and I refuse to deal with the headache of that lol. I use a clear and comprehensive contract that I found on the internet and personally could never imagine entering into an agreement (like a lease) on either side without one… There’s just too much money on the line in horse leasing for me to risk going in without some kind of “legal” coverage!