What is a word/idiom for 'unable to decide'?

Let's say I have an important decision to make and I can't decide between two competing things (like break up with a girl or not break up with her). What would be a word/idiom to express that?


Here are several choices: on the fence, indecisive, vacillating. I would use each one a little differently in a sentence.

I am still on the fence about breaking up with her.

or

I am indecisive about breaking up with her.

or

I am vacillating between breaking up or staying with her.


What about this?

I am torn between breaking up or staying with her.