I think my ex might try to harm me
This is terrifying. How do you think he's going to harm you?
I think he might try to stab me with a knife.
That is so scary what your ex can do, you need to run as fast as you can and go to the police. You can't delay in getting a retaining order, because he truly might hurt you. Your delay can mean the loss of your life.
My ex is pathetic, all he can do is gaslight me and harm me.
I know, and I can't stress this enough that you're in danger and you should really tell the police about him so that they can do something about it. I recommend that you don't go outside alone specially in the dark, so that you would not risk yourself in harm's way.