1、be in a dilemma
It seems you are in a dilemma.
2、You just can't get over... (you can't forget...)
The French soccer fans can't get over the World Cup 2002.
3、dwell on something
You should not dwell too much on your past failures.
We shouldn't dwell on someone's past.
4、prey on somebody's mind
The thought that he could have helped more preyed on his mind.