Its all about memories. Memories serve a better part of every relationship. You find that someone is almost giving up on the other party but when she recalls how the person has been good and how much time they've spent together going out on outings, makes them stick to the person. Also, a lot of people hate from jumping from one relationship to the other. They hence opt to stick around hoping they'll change. Also some people fear that when they move on,they might find other lovers who are even worse than their current. Finally, others just stick around because they've spent too much time together and they fear that they might not find someone else soon.