Yeah, the bromance is definitely an important part of the triangle. And the thing about Stefan and Damon is that they've sort of already done the triangle thing with Katherine - and it ended with Damon choosing Katherine, Katherine choosing Stefan, and Stefan choosing... Damon. Heh. And now the repercussions of that are playing out with Elena.

BtVS sort of did that with Drusilla, but the dynamics were very different. And although they had a similarly long history, Angel and Spike were never really in the position of choosing between the other and Buffy, not the way Stefan has. And that wrinkle makes it way more complicated than the typical love triangle "who will he/she choose?"