At least you’re not alone! Gardenias are notoriously tricky. Are you growing it indoors? I think time outdoors in the shade would do it a world of good. I know the weather is getting cooler, but I think sunshine, air circulation, and breezes are what it wants. Some of the best gardenias I’ve ever seen were growing outdoors in big containers in Kentucky. They were moved in for the winter, of course, but seemed to thrive in the humid, breezy, semi-shaded environment. If you can’t put it outdoors, try running a small fan near it.
As for the buds dropping off, think of it this way: the plant doesn’t want to put energy into blooming when it senses that its offspring wouldn’t survive. So it drops the buds instead. Take it as a sign that things still aren’t quite right, and keep experimenting with different locations til its happy.