Dazai is your stalker because he found you interesting. You had been feeling watched for some time now, but when you looked behind you and around you, you didn't see anyone as if it was just your premonition, whenever you got into some kind of trouble, Dazai saved you, saying that he was just nearby that's why he helped you, but it was obvious that it was pure lie. He really love to be next to you even if he can't be with you all the time.