beachgal,
You sound like you have a good head on your shoulders and have learned some important things very quickly that often take people a lifetime to figure out. Good for you.
Going back to the house you depledged - just chat and hang out with the girls you still talk to. It is possible that you will be more comfortable here than at the other houses, simply because you will be more familiar with the girls. If you really don't want to be here, don't let that confuse you. Also, don't mislead them into thinking you want to come back if you don't.
As far as telling the other houses you depledged, it depends on how much groups know about other groups. They might already be aware of your situation. If they ask why you didn't rush last year though, tell them the truth - "I got a bid to XYZ and began pledging, but it just wasn't the right place for me."