I never had the impression Jack twist was forgiving himself, i had the impression he had an AHA!! moment where he suddenly saw a part of himself very clearly, due to the acts and behaviour of another person...in this case the teenaged druggie. This is not so different from the AHA!! moments many people had after they saw brokeback.
There are ways and ways for a good author to keep a plot and story united during a time-lapse, let's not forget that.
What grabbed my gut was the reality of the goodbye, the reality of how both men behaved. This is something RARELY achieved in fanfic, where far too many simply post these silly [ to me anyway, as a guy] and completely unrealistic [ from the male POV] descriptions of a supposedly good lay lol, and the characters throbbing manly members are orgasming every 5 minutes while the men spout ridiculous things only a girl would want to hear. Seriously, most of the sex in fanfic has characters far more verbal then nearly any male i ever met lol lol lol, in positions NO guy would EVER think to say a word in!
These two breathe. They are so realistic it's awesome. When they have sex, it's real, when they talk it's real. They are characters you can and do believe, believe in and care about.