By mentally accepting that he might be ready for a family and new leash on life, Abraham was really understanding and re-embracing his former role as a father and protector.
(And really, Glenn was fake-killed prior to his legitimate death, so there are exceptions for all rules.)
And a true protector doesn’t play favorites, so this was indeed the mindset he needed to grasp onto in order to be able to look up at Negan with such conviction and bravado, with death just seconds away.
Many TV shows give certain characters a plot-based boost of character development just as they’re about to get killed off the show, and Abraham definitely got some of that, but there may have been a deeper meaning there.