Yes, it is all that. But why all that sadness and tragedy, those squashed hopes and twarthed longings and wasted lives should hold such a spell over such a long time..... it's a topic that belongs in the "Why are we like this" thread I suppose. But I'm still not sure that I fully know the answer.
Well, I think that tragic romances are essentially the most classic type of romance. It seems that the romances that stand the test of time (Romeo and Juliet... to name only the most obvious) and even classical romances (a la the Classical Allusion thread from TOB) are all about a core of sadness... or a bittersweetness. It's hard to think of a lot of great romances (literary or cinematic) that have happy, happy endings.
And, I've said it before, but I'll repeat it here. My very first reaction to BBM walking out of the theater after my first viewing was... "wow, they were lucky." Of course this is a profound tragedy on many levels- from the very obvious (Jack dies young - and maybe is murdered-, Ennis had a tragic childhood, they each spend a lot of time being lonely, they couldn't figure out a way to live together, etc.) to extremely subtle emotional tragedies. To me one of the biggest tragedies is how much time they lost by being apart so much. The 'never enough time' tragedy really stings for me. BUT, in the end there are little triumphs too. Even after he's dead, Jack is able to express his love for Ennis and reach out and comfort him - help him find a little closure -with those shirts. And Jack gets the commitment that he wanted from Ennis. Many people don't find a true-love like they had. And, eventhough their time together was fraught with separations... they still had twenty years of being in love. They made each others lives happy and exciting. To have had one kiss like the reunion kiss is something profoundly wonderful (and I think we can assume that they had more like that...).
I guess I'm preaching to the choir here... but there's really a lot of sweet with the bitter here.