I am afraid my prolonged sadness is affecting my children. How do I protect them?

Children do not need to be protected from seeing you sad now and then, but from carrying adult burdens that are not theirs to bear. It is fine if they see you sad; it teaches them that feelings are normal. What must be avoided is making them the people you complain to about their father, or a source of information about the other household. Make sure their routine is kept: meals, school and sleep as usual. Give them simple reassurance that they are still loved by both mother and father. If your sadness drags on until it is hard to function, get help from a counsellor for your children's sake and your own. Looking after yourself is part of looking after them. See mental health.