Cause of Split: Ross broke up with Elizabeth because he was annoyed by her immaturity. Ross and Elizabeth were incompatible from the start and never should've gone out for as long as they did. Student-teacher relationships weren't allowed at his school, and several faculty members reminded him about that to no avail.
Even after Elizabeth's dad, Paul, got involved and threatened to tell the school, they continued to date in secret. The number of fake breakups they used to hide their relationship made it even more frustrating, especially since they didn't really seem to have much in common in the first place. Their real breakup was also disappointing because Ross ultimately didn't even recognize how inappropriate their relationship was. Despite warnings from her friends and her company's dating policy, Rachel dated her assistant, Tag, while the two were working at Ralph Lauren.
Cause of Split: Rachel dumped Tag on her 30th birthday because she thought he was too young for a serious relationship. Rachel and Tag weren't as terrible of a couple as Ross and Elizabeth, but they were still doomed from the start, and their relationship was problematic given their respective jobs.
The situation was worsened by the fact that Tag wasn't even qualified for the position in the first place. Rachel only hired him as her assistant because she found him attractive. But somehow the Ralph Lauren rules against dating a superior weren't what led to their split. Like Ross and Elizabeth, Rachel and Tag's age gap tore them apart. By the time Tag returned, hoping to win Rachel back, she was pregnant with Ross' child, so he quickly changed his mind.
They probably shouldn't have dated under their initial circumstances, and outside of attraction, they didn't have much in common. Rachel inadvertently set Ross and Emily up when her boss asked her to take his niece, Emily, out for the night while she was visiting from London.
