Personally, I don't view it as a wasted emotion. It's one of the steps in the grieving process. However, maybe there is a more productive way for you to deal with it? Maybe take a kick boxing class or something to release some of that anger? You'd be letting off some steam plus getting in shape along with it. Bonus!
A tip that helped me when going through a D with my first H. Like you, I was angry that he abandoned us and only thought about himself. Instead of calling and screaming at him (which trust me, I wanted to do really bad) I would call the movie hotline at my local theatre and scream at the recording. Is that a little bit silly? Of course. Did it help? More than you know!
"Everyone you meet has baggage. Find someone who loves you enough to help you unpack." ¤Formerly DelinquentGurl¤