When you can't take anymore? Dad has deteriated fast, can't play along with the madness anymore and the stress has taken its toll.

Looking at the OP's past answers, she's been in this situation since 2017 and before.

It does get long, does it not.

Star, call Adult Social Care - you'll find the number on your local authority's website - and ask their advice. Do you actually have any formal responsibility for your Dad, such as Lasting Power of Attorney or anything like that?

If you are his one and only caregiver, then it's time to either hire some full-time help(with his money)in to assist him and give you much needed breaks, or it's time to be looking at placing him in the appropriate facility. Not everyone is cut out to be caregiver, and that's ok. You must do what's best for you. Best wishes.

There seems to be no information on your profile.
Does Dad live with you?
How old is he?
You say you are waiting for a diagnosis. Has he had testing done?
Is your father having dementia?
Are you POA for your father?
Without some knowledge of what is happening with you I can't imagine we can hazard an opinion or a guess. Can do nothing but say sorry, and hope things get better for you.