Oh yes, Robin and Barney really are dating when How I Met Your Mother kicks off its fifth season. But the pair won't actually put a label on their relationship.
Marshall and Lily give each other one horrified look in the season five episode, "Double Date." I guess you would too if you saw a version of yourself at a strip club.
How I Met Your Mother is the story of how Ted Mosby met his wife as told to his children. Yes, it's a very long story that will take many seasons to tell.