He can leave the seat down if he wants to but leaving you to clean up his bodily fluids is very fucked up. You’re not his nanny or his mommy to clean up after he has a little accident, and the fact that you’ve told him you don’t wanna do this and he clearly doesn’t care shows me that he does not respect your feelings
Yeah if you telling him repeatedly and he REFUSES to change, talking more than 3 times, it’s unlikely to change and will probably get worse as yall stay together longer. If you like him that much, telling him with more emphasis and see if he improves or snaps back first. If the latter, DIP ASAP.