I'm made happy by my cleaning, nobody else. 🤣🤣🤣
The main bathroom is used by guests so yes it matters if it's filthy.
And you're apparently the only who cares about how guests perceive this. I'm not saying I agree with him about that. But it should be clear to you by now that this is much more important to you than it is to him. No amount of nagging will make him agree with you about its importance.
I clean the bathroom and toilet I use, I also then have to go into a bathroom I don't use and do that as well. When they could just do it after their shower/used the toilet.
No, you don't "have" to. You choose to. I understand why you choose to, but framing this as though you have no agency whatsoever is counterproductive.
Mould is a health hazard.
Close the door. Shove a towel under the gap if you're that worried about it. Though if mould is popping so often that cleaning it whenever it appears is a real hardship, and you can't just spray something on it every few weeks, it's probably a bigger issue with the house itself.
Why is it me poisoning the well and not them by not upping their standards? Because you're the one making empty threats about divorce.
Reframe. Hey slovenly one, don't ruin your marriage over the floors and toilet, you know they just love a clean house, humour them, up your standards and just wipe piss off a toilet, it'll stop that whining and you might get laid.
It doesn't matter whose fault it is. All that matters is that you can't force him to do anything he's determined not to do. The only thing you can control is what you do about it. Clearly he's decided that getting laid (by you, at least) isn't worth cleaning the toilet. Which isn't terribly surprising if you're yelling about divorce all the time.
By all means, leave your marriage if you're so unhappy. That's your choice. Understand that, own it, and be prepared to live with the consequences either way. If you choose to stay, one of those consequences will be that nothing gets cleaned unless you clean it yourself. Either that's worth it to you, or it isn't. But if you choose to stay, the healthiest approach would be to try to find peace with the situation, not do everything in your power to make sure everyone else is as miserable as you are.