Is the issue here, "You told me you'll ruin me, but you stopped. What's wrong?" or am I missing something?
I guess it's been a while since last chapter, I had to reread it and check again...
The issue is Karin is not communicating what she wants and needs, focusing instead on what Hikaru wants to do. When they started going out Karin was a lot more assertive and pushed the relationship forward, but ever since she actually fell in love, due to her own issues, she feels like her love is less valid, so she's taken a step back, and Hikaru's noticed that.