How did <PERSON> and <PERSON> meet?
In Lord of the Rings: The Fellowship of the Ring, there were many parts which mentioned that <PERSON> knew <PERSON>, and had known him for some time. This is after <PERSON> met <PERSON>, fled past the Ford, and made it safely to Rivendell. In the time spent during and before Elrond's Council, many mentions were made implying that <PERSON> and <PERSON> were close friends.
"[...] you have disturbed me - in the middle of making up a song. I was stuck over a line or two, and was thinking about them; but now I don't suppose I shall ever get them right [...] I shall have to get my friend the Dunadan to help me."
-Bilbo to <PERSON> and <PERSON> (Many Meetings)
Suddenly <PERSON> looked up. "Ah, there you are at last, <PERSON>!" he cried.
"<PERSON>!" said <PERSON>. "You seem to have a lot of names."
"Well, <PERSON> is one I have never heard before, anyway," said <PERSON>. 381
"What do you call him that for?"
"They call me that in Bree," said <PERSON> laughing, "and that is how I was introduced to him."
"And why do you call him <PERSON>?" asked <PERSON>.
[...]
"Well, my dear fellow," said <PERSON>, "[...] can't you spare me a moment? I want your help in something urgent. <PERSON> says this song of mine is to be finished before the end of the evening, and I am stuck. Let's go off into a corner and polish it up!"
<PERSON> smiled. "Come then!" he said. "Let me hear it!"
-Bilbo, <PERSON> and <PERSON> (<PERSON>/<PERSON>) in conversation (Many Meetings)
All that is gold does not glitter,
Not all those who wander are lost;
The old that is strong does not wither,
Deep roots are not reached by the frost.
From the ashes a fire shall be woken,
A light from the shadows shall spring;
Renewed shall be blade that was broken:
The crownless again shall be king.
[...]
"I made that up myself," he whispered to <PERSON>, "for the Dunadan, a long time ago when he first told me about himself."
-Bilbo to <PERSON> about <PERSON> (The Council of Elrond)
So from these parts in the book, it is clear that <PERSON> and <PERSON> knew each other for a long time, <PERSON> trusted <PERSON> and told him his story, and they were obviously close enough that <PERSON> would be willing to help <PERSON> with his song, though he had other pressing matters on his mind. Even later, in The Return of the King, <PERSON> was even given an invitation to <PERSON>'s wedding, which they both had been waiting for, for some time.
However, nowhere in the book can I find the story of how <PERSON> and <PERSON> met, how they became so close, without <PERSON> ever hearing of him from his uncle, and especially how <PERSON> earned <PERSON>'s trust. Does anyone know the story between these two? 381