Mike is your best friend, so you kinda notice when he starts acting weird and disappears and reappears like it's nobody business, but what are you going to do about it, you can't just stand there and watch the darkness take over.
You start out as good. But, then you meet him. Jim Moriarty. He sees that darkness inside of you. The darkness you've tried so hard all of your life to hide. You push it down. You don't listen to him. But the ever persistent thought of giving into that darkness, is getting harder and harder to resist.
(I don't take full credit, some credit does go to @Galanator since it is kinda based off of a roleplay that we did.)