What.

yaoi logic （/TДT)/

Well, it's a common trope in yaoi manga. But he seemed to have always been insecure due to his self-image issues: first because he looked delicate and wanted to be tall and manly, and latter because he changed too fast and now is afraid he might have lost his charm. So in this case he is probably just looking for an easy excuse to break up. Self-sabotage is very common behavior in insecure people after all.