I will agree with you guys that the friendship should have been longer. I think I would have had the falling out occur in the next movie but perhaps they did it this way because they didn't anticipate that there would be another one and wanted to take care of in in the first movie? Something I thought of.
I've definitely thought about that. They weren't assured a sequel, and who knows, we might not see a sequel anyway. I think it was the filmmakers just tying things to the Singer movies in case we don't see a sequel. Kind of disappointing, I know, but part of the filmmaking process- you never know if you're going to be able to make another.