There were a lot of things different during that break up.
I mean, in Season 3 Brian and Justin practically constantly bumped into each other. Brian tried to hold contact, helped Justin, etc. etc. And in Season 5 there was nothing left.
Brian didn't even try to stay in contact, they couldn't even talk to each other anymore, it was just weird. And sad
And opther than the first break up, the second one truly felt like the end.