Not ready to say goodbye.

Hi there,  I am not new to cancer but I am new to it being one of my parents.  My dad who has always been a very strong man who worked in all weather as a very intelligent and worldly man was told at the end of January that he had a mass on his right lung.  This was worrying news and we were told that he would have a series of tests and they would figure out what type of cancer it was etc.  literally days later Dad fell over whilst putting on his trousers and also began vomiting.   His GP told him that he wanted him to go for an urgent CT scan on his head.  the following day dad went into hospital with brain metastases. The cancer has spread all over and is particularly large at the back of his head.  We also learnt that it has travelled into his spine causing weakness and numbness.   Dad also now has Covid.  which thankfully he has not suffered with too much, but my word his mind has!    We were warned that his personality could change.  We are just baffled at how fast this has happened.  he is fixated on bowel movements and how much battery life his phone has.  and he has started to be quite rude to the staff in the hospital.  This is SO out of character.    Long story short Dad is not able to have chemo/radiotherapy on his head.  So its a waiting game right?  has anyone else got first hand experience of watching a loved one change so rapidly?  and did they get back to normal closer to the end?  we don't have a prognosis I understand that the Drs. don't do this unless death is imminent. but Google has given us a pretty grim clue. I am just not ready to live in a world without my dad.