"You have to know that I appreciate our friendship like nothing else in this world, and I would do anything to make it up to you. I truly am sorry."
"I know I have not acted the way a friend should do, and for that I am sorry. I promise to make it up to you when I have the chance."
"I want you to know that I am truly sorry for all I’ve done. I value our friendship way too much to go around doing stupid stuff to you, so I promise to make everything up to you as long as you let me."