How can you tell how long you have been friends with someone on Instant Messenger?

I also want to know how can I retrieve old messages from years ago?How can you tell how long you have been friends with someone on Instant Messenger?
You could look at the History of your messages in the Instant Messenger, if you have saved them from last time. This will show the date of every friends you have chat with, including the time of chat.How can you tell how long you have been friends with someone on Instant Messenger?
have a memo and specified the date you first encounter him/her.