You're all figments of my imagination

Thinking like this will drive you insane, not that there is anything wrong with being insane. Being insane allows you to see and view things differently than other people and come up with new things. The fact that most geniuses are insane proves this.

Anyway, if I am part of your imagination and you're a part of my imagination who is the main imaginer?

"Insane" doesn't really mean much outside of law. Differences in culture or lifestyle (looking upon tribal civilization as a man of the new world, for example) can be seen as "insane", simply because we don't understand them.