Yup, watching from the sidelines can be painful but what other choice do you have? I can tell you that once you are living apart (although thinking of that is painful as well) it does become much easier. That's when we really are able to focus on ourselves and what we want for our new lives. Where you find yourself now is the hardest part of this whole journey.
Once you get used to being on your own it is an adjustment. Until you realize that you are now breathing easier and enjoying the little things again, then everything changes. There is a feeling of excitement realizing that you can make your life whatever you want it to be. There is no more living to keep the peace, or to make an unhappy person happy, because in doing so we do lose a part of ourselves, and believe me there is something to be said for not being held hostage emotionally.
So for now keep busy if that works for you, but also take as much time as you can with your kids. They need all of the security that Dad can give them.