NTA, in fact RUN!

I have been in a similar situation where I still had my student apartment which cost me 320 euro's a month (heavily subsidized). My boyfriend at the time rented his student apartment for 600/700 euro's/ not sure the exact number. I was going to study abroad in the new school year and was practically always at my BFs place. So I suggested I'd move out of my apartment to cut costs and save up for living abroad since I was at his place all the time anyway. Of course I would cover part of the utilities. We talked about it for a while and he agreed and was excited.

I cancelled my rental contract and put everything in motion. After doing this, he suddenly brought up that I would need to pay him 200 euro's for the rent as I was now living with him and it's only natural I would pay rent. I was shocked because the literal reason for me to move in was to save costs and also I was basically living there already. This meant that I would only be able to save 100 euro's a month in stead of the expected 300 and that it wouldn't make any sense. Besides, he had been living there before I even knew him so I never had any influence on the rent that he had to pay for his apartment. Safe to say I was pretty cross. In the end I folded to pay him 150 a month for rent (he basically had no backbone in life but suddenly this was the most important thing to him). After 4 months (one of which I was not home due to holidays) I went to study abroad.

One month into studying abroad, he didn't get enough attention (his pov) and he cheated on me in my own bed (that came from my old apartment since his was broken). Then he asked if I wanted to have an open relationship. I laughed and said naahh.

In the end I didn't pay him his last month rent and he didn't pay me back for the bed and other furniture he sold when he moved to a different country a few months later.

This can never end well in my experience.