I was excluded from a work party and I'm going to ask one of my best friends at work why.
That's odd, do you know why he would do that?
No, he tricked me into staying home by saying that he'll come to me after the party they were having at his workplace.
If it's not a place where you work then he had no reason to invite you. In fact, it probably would have been inappropriate for him to do so. Work parties can be fun, but this one wasn't for you.
I will still confront him.
Confronting him is pointless as your expectation to be invited to this party, that didn't involve you, was unreasonable. If you really want to have a party, perhaps talk to your friend and you two can throw one together and invite your other friends.