Inseparable
People thought that the train ride made them inseparable. They were wrong. It was the time when Harry refused Malfoy. Ron immediately fell a little in love then.
It grew every time the Great Harry Potter, the Boy Who Lived, The Chosen One, did something to show he loved the Weasleys.
Every time Ron showed a side of his true, fiery, Weasley personality, Harry felt butterflies. When Ron was singled out, with his hand-me-down everything's and his tendency to flare up immediately, Harry would spring to his side immediately.
They were best friends. The best you could ever hope to be. Girlfriends would come and go, but best friends are there for you for life.