Eeeeehhhh I don't really have an answer for you...
I guess maybe Neo just wasn't happy with the kind of person she was around Roman, and was looking for a positive change in her life. Unfortunately I guess that meant cutting Roman out of hers, to avoid slipping back into her old ways. Maybe that's just part of life? People change. Sometimes even for the better..
OR! Maybe it was just Tuksons sick side burns. Yeah, that's definitely it. Screw all that "growth as a person" crap.