You can take solace in one thing: there have been bigger "friend-betrayals" before. Four instantly spring to mind:
1) Vice President Thomas Jefferson pays a tabloid to vilify and slander his supposed-BFF John Adams... who was technically his boss at the time.
2) Lando delivers Solo to the Empire.
3) Hamlet's uncle, Claudius, poisoned Hamlet's father, the King.
4) Roger Sterling hits on Don Draper's wife (a fascinating and near-forgotten subplot).
You should feel betrayed. Because you were betrayed. No, the guy didn't quite freeze you in carbonite or kneecap your presidential administration, but the best man acted like the worst.
He should have done whatever it takes to make it to your wedding. If for whatever reasons he couldn't come, the least he could do is throw you a bachelor party, for both fellowship and contrition. He let you down.
The behavior is weird enough, in fact, that we suspect either A) He's pissed about something (and not telling you) or B) He has his head up his ass, is depressed, is self-absorbed, or going through some weird shit. In the case of A), maybe he's secretly resentful that you're not footing the bill for his cruise and this is his passive-aggressive revenge. Childish.
Regardless, here's what we recommend.
Do not "fire" him as a best man. This will sunder your friendship. Forever. It will give him the moral high ground and it will give you pangs of regret for the rest of your life.
You should have a bachelor party. Even if it means that you have to plan the damn thing yourself, the event will help close the wounds. You will be tempted to get all mopey and say to yourself in a 12-year-old voice, "Fine, if that poo-poo-head isn't my real friend, then I don't need a stupid bachelor party anyways." Snap out of it. You need a party. Don't succumb to your 12-year-old instincts.
Tell your friend that if he refuses to be the planner, fine, but since you do want a party, you're asking your other friend, Bob, to plan it instead. Bob can be a groomsman or another friend or whoever else is next in the pecking order. This way you delegate the best man's responsibility to someone else, while nominally keeping your friend in office.
Invite the best man--don't freeze him out. Yes, he let you down, and yes, you have every right to shun him from the party, but extending the olive branch will help preserve your long-term friendship. And hell, even Lando came around. Hell, even Jefferson and Adams resumed their friendship with years of written correspondence.
Hope this helps. Good luck.
(P.S. Claudius and Hamlet's dad... not so much.)
For more on this topic, see: When the Best Man Isn’t: When He's Derelict in His Duties.