M - You are doing a great job in a very tough situation. This week will be really difficult for you.
Don't look at it as letting your H off the hook. I have struggled with this a lot. H is getting to enjoy the life that he wants, while I put on a smile and pretend like he did not crush my world. I have come to realize that I am not letting him off the hook. I am actually giving myself permission to not let H's actions define me and allowing myself to move forward. Hanging on the anger and resentment will not change your H and will only cause you to be more and more miserable.
I think that detaching comes with time. It will be easier once H has moved out. You will learn that you will be ok on your own with the kids and that will give you confidence. The more confident you feel, the less you feel the need to grab onto your old marriage out of desperation. One night I found myself laughing hysterically with the kids before bed, looked at their smiling faces and thought, we will be ok no matter what happens. I had been telling myself that for weeks, but this time I actually knew it in my heart. It has changed the way that I look at H and the way that I let his actions affect me. I still have setbacks, but I can feel things slowly changing. Just remember that it is not going to happen overnight, especially if you have to see H often due to the kids.
I think that you mentioned that you like to be in control and to fix things. I am the exact same way. Since I cannot fix H or our M, I has turned my attention towards finding things to help myself. I have been reading anything that I can get my hands on. It occupies some of my time. It also makes me feel like I am doing something. Try to focus your energy on you and just let you H be for now.