Thats not crazy, its natural--any good owner will have to deal with that loss. When you care for animals properly, they are almost like your children.
Everyone deals with grief differently, it really depends on you. I'm a reader, so I would go and read books about people and animals...Marley and Me (is about a dog, but still) was one of my favorites--about how quirky animals can be, crazy and silly, but you love them despite (and sometimes because of) those things. I have friends who are artistic, so they will make collages of things they used to do with their critter, or pictures of them. Others will write down great stories about things that they did. They point is, you need to honor their memory--think of all the great times, the funny times, the ridiculous times. The things that made him the great kitty he was. And don't forget--as much as we choose them, they choose us, too. You thought he was the best cat--I bet he thought you were the best human.
Good luck. There is no simple solution, unfortunately. It will get better, though. You will always miss him, but the pain does lessen.
animal lover/owner for many years--I've lost several critters, and its never easy.