How long ago did the 1st piggie die? Very 
My DD had two boars - one died in July (he was ill for 48 hours but even though we saw the vet, he died) the other GP was with us as we cuddled the ill boy (DD, myself and the 2 pigs sat on the bed )
The remaining boar (GP1) is now 3.3 yo.
We had a very hot summer, his brother died, we got a new male piglet a few days later (who he gets on really well with and made a huge difference to his wellbeing) and went to Small Animal Boarding when we were on holiday (piglet was about 12 weeks when they went on holiday)
He lost weight, he's slowly regaining a bit. But he feels 'middleaged'. A bit bony. A bit saggy. A bit jowly. A bit arthritic (though he did have a fall when he was younger too)
And our new boy is huge, solid and muscular so the difference is more stark.
They can go either way TBH. They can be bribeable and cossetted. Or they can go downhill.
Lots of attention, put him where he can chat to you . A radio when he's alone?
When our GP1 was alone he slept in my DD room in his cage, but it was too warm and stuffy for him to stay there , so he went out by day to the Pighouse. I was really
for him alone all day.
Are you considering a new pig? How old is your boar?