So I have CPTSD from my abusive father, who i don't have contact with anymore. And this time last year my mom, my fiancee, and I moved into my mom's bfs (D's) house. Now I have a delusion that somehow my dad is going to take over D's body. Like my dad is going to morph into D and replace him. Now when D talks to my mom it's hard for me to distinguish his voice from my dad's. I can't imagine if this delusion expands farther than just voices. I don't want to hurt D but I feel like I would if I suddenly started to see my dad's face in D's.. 
What do I do? I've resorted to staying in my room for most of the day so I avoid him. But that's not really healthy for my mindset.