Some people would think Isaac sacrificed himself so that when Mr Skelly reincarnates he would treat next life Isaac better. But for me, I think that Isaac acknowledged Mr Skelly as his friend and that Isaac never had a friend for over 200 - 300 years so Mr Skelly being his first friend after so long may have made Isaac attracted to him in a way since Isaac told him the 'next' time they meet, they should be more honest with each other.