I think DE was somehow magnified in Jack's mind precisely for meaning such a great and cruel contrast between what they were living then and in the moment they had the LC.And I'd add between how they were living then and while Jack was remembering it; when they were in BBM,they felt free,in love,with all the strength to face the whole rest of the world,that,on the other side,was far away from them.After LC,on the contrary,they had finished all their strength,because the world,the society has won them and made them feel slave of their environment and,sometimes,of their own feelings-specially in Ennis case-.When the difference between what the moments we lived from illusions and hopes and the moments we lived from memories is so brutal,all of us tend to hang us on our old dreams,these hopes that have turned into bitter truths.And in the middle,there's always some fantasy we put on them,because we need to believe everything was better still than it was.Even if BBM moments were paradise on Earth for both of them... :\'(