B.W.
An abrupt stop in nursing is a strike, and it will pass. He may be stubborn and hard headed but right now you need to hold out and not give a bottle. He's looking for the instant gratification, and at around 3-4 months is when your milk rreally stabilizes and doesn't have the forceful letdown, its a nice easy flow, and he has to work for it, hence his frustration. GIving him a bottle will only feed this need for fast flowing milk, since babies don't have to work much to get the milk to flow.
Keep offering througout the day at his usual nursing times. Before you nurse, try to get 'in the mood' by thinking of him nursing, that should help stimulate your letdown as well.
But mostly you'll just have to stick it out, he'll settle down soon enough, nursing strikes are common this age and its NOT weaning, its a strike. He'll come back, just keep offering. Your milk supply will be fine, just don't offer bottles in place of nursing.