I've got a bathroom that has a single switch in it that operates both the bathroom fan and the light fixtures. I'd like to separate the two to run on their own switches.

After turning off the power to the bathroom, I've opened up the box containing the switch to find 4 sets of wires. Each set has a white wire that have all been twisted together with a wire nut. I'm pretty sure theses are all my neutrals. This leaves 4 wires that have all been painted black and white. These 4 wires are twisted together in pairs with another wire nut and each of those has a 3rd wire used to connect to each end of the switch.

Here is where my confusion begins. I assumed that the 4 black/white wires in the box went to (1) Source of power (2) lights (3) fan (4) additional power source (realized this was wrong pretty quick). I purchased a double switch and hooked up (1) and (2) to switch1 and (3) and (4) to switch2. I turned the power back on and flipped switch1 to find the light and fan come on. Next I flipped switch2, which did apparently nothing. Using a wire a tester I quickly discovered that (1) is correct, (2) lights/fan, (3) no clue, and (4) goes to an outlet in the next room. I also found that in this configuration that turning on switch1 and then switch2 activates the outlet in the next room; however, turning on switch2 by itself does nothing.

So, my questions are:
(a) Can someone explain how these wires are probably hooked up and what in the world have I done?
(b) How do I hook the wires back up in the time being? Right now, I believe that (1) and (4) should be connected together and (2) and (3) should be connected back together. And the pair of (1/4) should go to one part of the switch and the pair of (2/3) to the other.
Finally,
(c) How can I accomplish my original goal to separate the fan/light

Also, thanks in advance for any insight or advice.

Light and fan are now on their own switch. I think I probably would have had it right the first time if I had bothered to read the back of the new switch. Apparently this whole time I had it wired backwards, which explains why the light/fan still came on when the top switch was turned on. (1) and (4) were hooked up to the sides marked a and b while (2) and (3) were hooked up to the sides marked common. Oops. Common was also linked together with a metal tab, which should have been a give away.