Hi there!

English is my second language, so I'm going to use your site a lot -- I'm glad that I found it. Thank you!

A boyfriend has sent me a note and said something like "keep it real..." - don't know what does it mean...

Thank you for your time,

the meaning of "keep it real" is :-

be true to yourself, honest

Whenever I don't understand an expression or a word used by my peers I turn to www.urbandictionary.com.
It's a dictionary that is basically maintained and fed by the users who crawl it for information, that is to say that you can find almost any slang or colloquial expression in it.
Give it a shot, it's useful and fun to read.