1、be in a dilema
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.
5、take something to heart
Don't take such small things to heart.
My heart is being torn in two different directions.
7、on the fence
I'm on the fence.
8、the lesser of two evils
It was considered that this alternative would be the lesser of two evils.
Neither candidate seemed capable of governing the country. People voted for him as the lesser oftwo evils.