bei's actions are very much justified...
bei did everything he can to get in a relationship with yiming for 8+ years. nothing worked.
even after them doing the deed, yiming still labeled bei as "just a friend".
when bei and yiming were just roommates back then with second+third bro, bei knew yiming hated gay people.
so it would make sense for bei to assume yiming was just lying, and making fun of him.