The way I finally decided was to do a pro's/con's list. I listed all the things that were good and beneficial on one side and the bad and negitive stuff on the other. A few things to keep in mind...

You cannot keep a relationship going by yourself.
A marriage will not work 'for the kids'.
You cannot make the other person change...

You MUST be sure that you have tried everything before you will feel ready to go on. Divorce is not easy; it is not fun. When your relationship is truly over, it is a relief and a good thing, however. You will know when it is truly over. In your heart, you WILL know.