If you believe the lies that evil (Tulpa) tell you, you will invite them in. Once you have done that, they, NOT you, have control. I first heard about Tulpa 40 years ago, I would say I understand them pretty well. Back then, the name was interchangeable with demon.
Okay. But my delusion will NOT be a demon, and Severus won't tell me lies or truths, he'll just be a man who lives with me but he will be just an imagination, and the people who say that Tulpa means demon are wrong... And the things what they say about Tulpae are not true. I study Tulpae and I know almost everything about Tulpae. I also know one Christian person who has a Tulpa and his Tulpa never caused any problems, and another Christian said that creating a delusion is not a sin. And my priest also says that the Tulpae are just mental things, and nothing spiritual, paranormal/supernatural or witchcraft/occult/New Age.