well, "relation" means some connection between the things, and also a close set of people, usually the same blood.( in this meaning the noun "relation" is countable) and "relationship" means a special type of communication between two people,if they are in love with each other. for instance: My close relations are coming next week. This text doesn't relate to our topic. I have pretty nice relationship with Dan!

A relationship is, for what I know, a romantic bond between a man and a woman, that happened to start while cruising, possibly over calm waters, vastly separated from any trouble. (a.k.a. relation-ship)