A person can ask for forgiveness and their sins will be washed away but if they just continue doing the same bad things, forgiveness is moot, eventually god gives them over to uncontrite hearts. (romans something lol)
Judas walked with christ for 3 years, he was always the complainer, scoffer, scorner, who, as it is noticed, never had a good thing to say.
I don't really accept that judas wasn't paying attention in class because with jesus teaching of forgiveness there had to be a change of life, a true repentance that leads to that person turning their life around and undoing all the bad, in short, becoming a new person founded on the belief system of jesus christ. Judas was not about to change himself or his life and he knew that, so asking forgiveness or repentance was out of the question, therefore he hanged himself out of the despondency of his evil, self condemning heart.
Like most of the unsaved worlds population, they choose to disbelieve and like judas, one day it will be too late.