My OCD is telling me that God is the cause of my condition. I know it’s not true but it won’t leave my mind.
Satan is allowed to test us.
"My grace is sufficient for you, for My strength is made perfect in weakness." (in 2 Corinthians 12:7-15)
Paul had that thorn demon "messenger of Satan" messing with him, and it would not go away, even though Paul pleaded "three times" for God to make it go away. And Paul had such faith to do healing miracles and cast out devils; yet, he could not make that "messenger of Satan" stop messing with him.
But then he had a little talk with Jesus. And Paul learned to submit to God in His grace which is almighty to keep us safe from any effect of Satan's evil spirit, while also making us guaranteed to succeed in doing whatsoever God's grace has us doing.
So, a basic, I would say is do not let that evil stuff decide how you are or what you do or where your attention goes. And a trick is how Satan is trying to get us to try to control him or a person or a problem. Instead, we need to be attentive to how God wants to share with us and guide us.
When paranoid stuff comes my way and won't go away, first I usually get into fighting with the imagined person who is messing with me in my imagination. But then it comes how I am not loving that problem person the way Jesus wants. So, I trust God to correct me so I am submissive to God in His peace > Colossians 3:15.
In His peace I might get enlightenment about the person. And I become caring in prayer for that person. And then I am ready to find out how I do when that person is with me, however. And usually things are not at all the way I was imagining, at first.
Practically, when I imagine trouble with someone, it might help to say, so you're going to do that. We will see. God is in control. You're going to have to prove it; I'm not doing anything about you to try to protect myself or report you or control you; you have to prove what you claim you're going to do to me or whoever, because I can't prove you will do what you say. Also, I address the evil spirit who is bringing the imagination, and simply say Satan you are defeated by Jesus and His shed blood on Calvary, and God is in control of what you will or will not do, and we will see what really happens. So, we rebuke you and refuse you and resist you in the name of Jesus ! ! !
And instead of trying to figure out how to handle and control the problem person, be attentive to submitting to God in His peace.
"Therefore submit to God. Resist the devil and he will flee from you." (James 4:7)
Now, of course, what you are going through is different. But I'd say know it is an invisible being of Satan messing with you, and trust God to have you attentive to Him in His peace, and keep attentive to God and all He desires to share with you.