I think birthdays and holidays are just emotional times to begin with. They can even be stressful for people. Throw on top of that everything we deal with with alcoholism and addiction, and it's completely understandable that his cards have you balling your eyes out.
That just sucks that he sent those things to you. He can't make up for all the Bull$hit I'm sure you've had to put up with by sending you a frickin' card!!! I say Burn it (in a safe way) and delete the others. Then, go into the bathroom and scream your head off as if he is actually there. It helps when I do this and use a lot of cuss words.
Try it, you'll feel better.