I am sorry you are going througn this. i think your therapist is going to be your most valuable asset going forward because the process will be hard. I am in a somewhat similar situation but I am having trouble making the final cut from my husband. It is a very scary feeling to make the decision to leave a marriage. I have found a local support group, run by a therapist, for grieving separation and divorce. Very helpful to talk to other's who are going through the same thing.
I don't have any thing to say that will make this easier for you, but know that you are not alone and we are here to help support you through the process.