What people are totally unprepared for when a breakup occurs is the vacuum.
Now a spot that has always been filled is gone? That hollow feeling, which repeatedly screams something-is-missing eats away at any resolve that constituted the breakup originally.
Vacuums are uncomfortable. Change is uncomfortable. Being a free ion probably is uncomfortable. Whenever there is a need to break, whether it be with a career choice, a significant other, a geographical location that is loved, anything that we considered ours and part of our identity ...now missing, gives us that hollow feeling.
Some people are so distressed by it that they will return to a bad situation just because it is better than the vacuum they feel inside. Abused women and children have been known to do this, men return to a bad job all because their identity can not stand the vacuum. Their identity has been painfully depleted.
This is when an imagination is important. Create a new you. That image might initially be missing a leg, but it will walk. That hollow inside is very noticeable but you have to remember...Nature abhors a vacuum. Something will come fill it. Be cautious what you let fill it, because usually it is very nearly the same as you escaped.
We often do that. Grab the familiar, and put ourselves in the exact same situation. I do it as well. (gasps)
Vacuums are opportunities to choose again. Remake yourself again. Being comfortable with a vacuum is a difficult thing. I wish I could give you an easy solution, but I can't. Recognize the vacuum. Mourn the lost, and be very choosy as what to let replace it.
Life wouldn't be fun if it were easy, so enjoy the journey.