It’s very sad for the young man that he has little idea how to look after himself at age 25 and continues to wreck the house because of his heavy handedness.
It’s now become an even more difficult problem for you to have to help him with.
I really think it would be a good idea to take on one challenge at a time and break the tasks down into small steps. Start at the bottom of the step ladder, with the easiest bit, demonstrating how you want it done and only move up a step once he consistently gets it right.
It’s possible that you thought that him moving out the first time would teach him all he needs to know to live well, - by some kind of automatic, magic process of metamorphosis into a life skilled, competent man. Or that his gf or flat mate would shame him into competency. But that doesn’t work with some SEN people and I think as his parents, you might want to give him a last chance …and start again with helping him learn life skills properly.
If you ask him to leave he simply won’t as he doesn’t know how to.
If you organise his leaving for him, he will still fail at practical life anyway and be back.
So really, what choice do you have if you care about him, but to persist in an orderly way that allows you to see the extent of his problem and get outside help or allows you to see progress towards independent living.
If he refuses to engage or to attempt to help himself, or becomes aggressive, then at least you will have given it your best shot before showing him the door. He will then have to learn to live with his own filthy, unhygienic habits.
You sound as of you could be ready to skip to that stage already?
So, if you can face it, make a list of problems he causes you in every day life.
Then break the problems down into smaller tasks that he can be taught to overcome. Start with hand washing … and the rule that he washes his hands as soon as he enters the house.
But before you start on the actual tasks, prepare him first for what’s about to happen. Tell him what he will be learning in order to live decently.
Spell it out to him, in writing that this is his last chance to engage with you in helping himself gain practical life skills and he must engage with you both. Also spell out to him in writing the consequences of never learning how to look after himself properly. And that he must pay for his door to be mended, pay for the broken bin etc and pay rent and bills. (By the way, don’t keep buying the same flimsy pedal bin …make him buy one that is more sturdy that can’t be broken and make him use that one rather than the pedal bin which he repeatedly breaks)
Life admin is also a task he needs to learn which you could help with.
Once you’ve got him sorted, maybe you will all be happier.
Only you know if it’s worth the effort of really trying to help him, or not.
As for sex, either do it quietly, or get creative or play loud music or plan together to grab an hour or two during the day when he’s at work. I’m a bit astonished that you have to ask.