20HE LEFT BONNIE BECAUSE SHE SHAVED HER HEAD
Ross is really good at a lot of things but being a good boyfriend isn't one of them. For the most part, he's sweet and caring but he has a tendency to be petty. Ross dated a long list of beautiful women but can still find a number of flaws.
For instance, he once dated the gorgeous Bonnie. She wasn't just pretty but was also fun to be with. He was really into her until she shaved her head bald. All of a sudden, he wanted to break up with her.
Although, getting back with Rachel might have had more to do with it. Regardless, he puts a lot of importance on looks. To be fair, bald is beautiful too. In fact, Bonnie could have made that look work. On top of that, her hair would have grown back eventually.