How do you get a guy to stop chasing you?
Dear Bitch,
No, you're not being a bitch. Your friend is being annoying and you need to give him a reality check. Tell him in a real serious voice without laughing or smiling that you are not interested in him, that his persistence is making it hard for you to stay friends with him, and that if he respects you and wants to continue being friends with you, he needs to cut it out and take the option completely off the table.
Now that ball's in his court. If he fixes his behavior, cool; move on. If not, unfriend him. You're not being a bitch. You're honoring the personal boundaries that he's ignoring.