From all you said, I do agree. I think you are in serious danger. You may think you have a platonic relationship but he’s obsessed. There is nothing healthy about the situation.
I’m glad you changed your locks. I’m not at all confident that is sufficient. I’m worried. If you withdraw from him, he may well escalate. I think you need more protection than a lock on the door.
Please don’t try to handle this on your own. You’ve never been in a situation like this before so, of course, you don’t know what to do. But the police and crisis teams do have experience to draw on. Talk to people who can offer you the protection and practical help you need. Do consider staying somewhere safe while you work this situation through.
By writing to us and by changing the locks, you took some important first steps toward self-preservation. Now, please, take the next one and go talk to the authorities.
I wish you well.