(SPOILERS FOR NOUGAT BEST ENDING)
If you do Chihaya's best ending, you sort of learn that he feels the MC deserves better than him. He's still possessive nonetheless and desires the heroine to an unhealthy level, but he's aware he's scum. I think in the ending where the two break up, it's implied that he lets her leave for those reasons. I may not be entirely right, but this sounds the most plausible to me.