nanabird
Does he drink to excess - has this been a habit for any length of time?
His mental and emotional see-sawing - being seemingly indifferent one minute then sort of caring the next... fits with one of the very common side effects of a damaged liver - Hepatic Encephalopathy. This is basically when the toxins that are normally processed by the liver enter the blood stream and then break the blood-brain barrier and into the brain. This causes multiple effects - one of which is seemingly emotional indifference, combativeness, impulsive behaviour, and a host of other mental and emotional issues.
Loss of interest in appearance and personal hygiene are also part of the effect of Hepatic Encephalopathy.
If his liver is damaged - this just might be the cause... a loving and affectionate partner can change into a cold and unfeeling person.
You say that he came back from the rock concert "exhausted" and seemed "strange" and you appear convinced he has cognitive problems... these, again, are all descriptions of people with Hepatic Encephalopathy.
I've had experience of this myself - so just wanted to put it forward as a possible explanation for his peculiar behaviour.