In an episode where he sees how close Chandler and Monica are, he dreams of himself and Monica in the same way.
Joey takes this very hard and admits that his role on Days was the best thing that ever happened to him.
In one episode, after persuasion from Rachel, he reads Little Women and she reads The Shining.
A good start is comedy improv.
This argument culminates in them nearly marrying out of spite until they make up when he admits to her that she is the first girl he has ever wanted to marry.
When her relationship with Pete ended, Ivy turned to close friend for comfort.