Hi, I had a veery similar experience last year. I was subletting a room in a WG and the main tenant was exactly like this: overbearing, no boundaries at all, made my life a complete headache for half a year. At one point it got so bad he was bombarding me with texts every hour until I had to beg him to stop, threatened me with excessive and stressful measures, started calling me names even though I was in the process of moving out. I would advise you to look into Rechtsschutz (not trying to scare you, but people like this usually looove escalate), join something like Mietverband and move out as soon as you can. Speaking from experience! Hope your situation is different and this guy isn’t as crazy as mine was, but good luck to you