If I'm not totally mistaken, this isn't possible.

You can't play shared games from other peoples libraries when you have that game yourself. Thus, your friend can't play CS when you're playing it.

Keep in mind, that family sharing is to allow others to test-play your games in hopes they will buy it afterwards. Not to enable you to play your games with friends.

Actually...

Yes, it is possible. But it involves using a loophole in the family sharing system.
Just remember that your first gaming owning friend cannot play on his account without kicking you off.

What you'll need:

• Two alternate accounts (They do not have to have anything owned on them)
• Two accounts that own the game in question.

What do you do:

1. On each computer that you want to play, log into the alternate accounts at least once.
2. Setup Steam Guard on both accounts as accounts are ineligible for family sharing if they do not have Steam Guard.
3. Log into the accounts that has the game in question.
4. Authorise your current computer for Family Sharing and authorise the alternate accounts you created.
5. Log out of the accounts that own the game on both computers.
6. Start playing on the alternate accounts!

Side note: This only applies to the OP's case.
Since you're playing Counter-Strike: Global Offensive, weapon skins and matchmaking is unavailable to those who do not own the game, or are playing via family sharing. However, you'll still be able to connect to your own server, if you create one.

For your case:

Note: Just to not confuse with who is who, let's say your friend who owns CS:GO and isn't playing is Friend 1 and the one who doesn't own but wants to play is Friend 2.

1. Both you and Friend 2, create an alternate account and setup Steam Guard.
2. Both you and Friend 2 then log into your alternate accounts... Then log out.
3. Get Friend 1's credentials and log into his account.
4. Give Friend 2 your credentials and get him to log into your account.
5. Both you and Friend 2 then go into Settings > Family > Family Sharing.
6. Both you and Friend 2 then authorize the current computer and the alternate accounts.
7. Both you and Friend 2 then log out of the accounts that own the game and log into your own corresponding alternate accounts.
8. Start playing [on the alternate accounts].

Alternatively

Can't you just use your friend-who-owns-the-game's account while your friend-who-does-not-own-the-game uses your account?

I don't 100% know if this works yet, but my buddy lent me his steam info when I logged into his, I noticed his games and my games that he didn't own. So what I did was install some of his games on my cpu and went back to my account, and so far they are downloading correctly.