Cass,

I have had the boys living with us for the last six years too. You are right, some days it is just like we are a big happy family and others everything falls apart.
Have you talked to your DH about how you are feeling? I know when things get very bad for me and I am not handling the boys (or their mother) too well, I go to some form of counselling. Is this an option for you?
Cass, the fact that you are feeling horrible about your feelings, is a good sign that you do care alot for these children, that you want to change things for the better. Hugs.