I know someone who uses olive oil because it has less cholesterol.
He says not to overheat it.
Oil better than butter. No water and no separating, as mentioned.
Straining very important. There is no thc left on the leaves, so there is no high left, and no sense leaving it in. Straining also removes the useless plant matter, which really helps diminish that kind of yukky taste.
Here's a link so you can do some harmless research before trying it.