I feel the same way more often than not. My self assessment is that it is because I have not fully detached yet.
My "good days" are when I fully accept the reality of my W being gone, really accept it, as opposed to having expectations or any other measure of attachment. The really tough part is stringing together those good days. Or heck, even sustaining an entire good day straight through.
Going out for me has been OK (GAL and all). But I never feel truly better unless my head is in the right place (e.g. detached.)
Very hard indeed.
Me: 30 W: 25 D4, D1 Undiscovered EA/PA since 6/2014 BD: 2/6/15 Living together - in limbo