When to let go

I recently read when Sandra Bullock found out about her husband, Jesse James affairs, she immediately left the house they shared together and moved somewhere else.  For many weeks we heard from the media and on shows like TMZ that she was filing for divorce, then she wasn't filing for divorce, they were getting back together, they weren't getting back together.   It wasn't until months later she came out with the story of her adopted child and the fact that she indeed, had already filed for divorce.
My question is when is that decision made?  Did she decide right away?  My problem is, I cannot decide whether I should actually file for divorce.  Honestly, I don't know what I'm waiting for.  I guess somewhere in the back of my mind I keep hoping that he will change.  I know how absurd that sounds.  I sound like a women on the Maury Povich Show.  The kind of women that Maury says, "we caught your husband with a decoy, you caught him in bed with another women, why are you still with him?  and the women answers lamely, "cuz I love him Maury." and the whole audience goes crazy and thinks she's a dumb b**ch.

That's me.  A dumb bi**h! My circumstances have not been exactly the same.  I have never actually caught my husband physically cheating.  I have caught him on the Internet on some singles website, chatting it up with various other women on numerous occasions.  I have caught him emailing another women about how much fun he had when he pulled over on the side of the road in his big rig and she came out to meet and make-out with him.  I have caught him giving out our address over the Internet.  Physically I have not caught him in the actual act.  He says it was just talk and he didn't mean anything by it.  I guess I'll never know.

I have spent the last six months in therapy.  An appointment my husband forced me into making stating that "it's all my fault and if I don't go to therapy to find out why I'm so bitchy then he's not coming back."
Therapy was a great idea, and I thank him for making me go.  What I learned, was in fact, it is not ALL my fault, and any other women, giving the same circumstances would probably be bitchy too!
I have listened to my husband blame me for everything.  The list is so long for things he is blaming me for,  that I would just rather not itemize them.  Suffice it to say that it boils down to, "I was mean and treated him bad."
But here's the thing, it's very possible I was mean.  Honestly, I really don't know who wouldn't be.  My husband spent more time on the Internet, sleeping, and hanging with his homies then he ever did with me, my daughter, or my step-son.  Let alone spend time with my two older kids.  He has continued to really just go way out of his way to be extremely verbally abusive to me.  He has continued in the lifestyle that got us we we are today.  The things he has done to me personally are so foul, I just would rather not tell anyone.  It's embarrassing. I have told my therapist who tells me "I have every right to never speak to him again."
So why haven't I filed for divorce?  I mean, do I really think he is going to change? And how much more insults and assaults toward my character, undeservedly disrespecting my parenting, and phone calls to my family should I really tolerate before I give up?
I would really love to hear your comments if you have had a similar situation.