According to this episode, Bart's favourite song (or at least one of them) is "Love Stinks". Considering how many relationships he's had over the series and how they have all ended, Negative Continuity or not, is it any surprise?
Arguably, the town indirectly shot themselves in the foot- they were so desperate for any type of positive news that when the team merely made it to the finals, they were celebrating as if they already won it all. Flanders was warning them this would give the team a swelled head, focusing on the adulation of the crowd more than the task at hand, and the whole episode might not have happened if they were smart enough to just wait until they actually played the game to celebrate. This being Springfield, though, it seems they just never learn.
Even without the attempted suicide, "The Joy of Sect" confirms that Springfield will react to loss very violently, meaning that Bart would've been killed by the townsfolk had Marge not called them out.
Though well-intentioned, Lisa's solution to Bart's trauma could be seen as Blaming the Victim, since it corrects Bart's failing rather than Springfield's attitude toward that failure. The result is that Bart walks away with the belief that he succeeded but without any confidence that others will continue to love him if he fails, and the only lesson he learns is that the basic decency of virtually everyone around him is conditional.
