Often times, the energy needed to maintain unhealthy relationships is grossly disproportionate to the energy needed to start over.
Fear is a common denominator in that complex bridge-burnin'-esteem buildin'-decision-makin' process. Fear of hamstringing future career opportunities, bruising social networks, etc.
While every situation is unique, the common question, regardless of circumstance, needs to be, "Is it worth it?" Only you can know for sure.