I'm going to get with the girl my friend has had a crush on for a long time.
How do you know he likes her?
He told me so and nobody can keep a secret from me.
You're going to cause a lot of tension between you and your friend. I don't think pursuing this girl is worth betraying your friend.
Screw him and his crush. I know what's best for me.
Well, a potential relationship is likely worth far less than a best friend.