Lovable Siamese, with a few issues

Casper is a lovable sealpoint siamese, that i've had almost 2 years. in the past year, he has begun to pee in my bed randomly. He even Pooped once. He only does it once every few months, but i can't figure out why. I change his litter box on a regular basis. Last week he peed in my bed 2 days in a row. Please help me understand why my cat is doing this. He is the sweetest most loving cat i've ever known and i can't help but feel he must be mad at me for something....but what?

Honestly the first thing I would do is get an appt with the vet to check for any urinary problems. This is usually the # 1 cause of peeing outside the litter box. If the vet sais all is okay then I would look into some behavior issues.
When a cat is stressed or upset it can trigger behaviors like this. You would need to look into the situation at the house. Any new cats show up when this happened. if so, it could be a personality conflict between the two. Then you would need to try and get things worked out between the 2 cats.
Were there any changes to the house? Any moved furniture the cat is partial to? Any new or strange smells? Any outside cats hanging around? Any change in work habits or routine?
You also need to make sure and get rid of any urine smell. If he still smells it, he will continue to go there on a whim. You can try the natures Miracle odor eliminator.

We moved recently, but it was over a month ago, do you think that could do it?

A move is enough to stress a cat. You said that he's been doing it for a year though. Does he have any problems with the other 2 cats at all? Also, is anyone in the house altered?