You are trapped in focusing on him and you need to stop. As my DB coach Chuck said, I need to do something for myself. Get a hobby, take dancing lessons, take a mini-vacation somewhere you have always wanted to go, something that is not a negative outlet to start something new that is YOU!
I know what you are going through. My W has left so many areas easily traceable and viewable not to mention I used to drive by her EA place to see if she was there. I also drove by a couple of times at the coworkers house she is staying at (not an OP). When I asked my W what she needed from me and she replied complete and total separation, I decided then and there I would stop checking on her in all areas. This has been difficult because she bought a new car, set up accounts with our insurance company, uses a cell phone I pay for on my account (I can retrieve text messages any time since the account belongs to me) and so other areas, if I WANT to. I could've been a private investigator with the number of ways I could track her. But it serves no purpose. It hurts me more than her. This is hurting you and your daughters. Let it go.
You cannot do anything about him. Consider him a lost cause for now because he is. If he comes back later after you have had a chance to work on building yourself back up to who you should be, then great. He will be even luckier than he was before he left. At the same time, you will have a better marriage because you won't need him, it will because you want him. Big difference.
Stay strong. Find a positive distraction. Avoid destructive outlets or behaviors at all costs. You can do it. Do it for your self and your children.
Me:56, W:51 D:26,S:24,S:22 Married:18 Bomb 9/27/06 Separated 11/27/06 Divorced 10/6/08 Leaving it up to God