The best friends who have been together since childhood are forced to separate and reunite after a long separation. They can fall in love if they want to, and they can really not separate if they want to.
They never wanted to separate. Even if they didn't have love, they still had an inseparable family relationship. To separate them would be to separate their own flesh and bones. They must stay together no matter what.
The deputy CP also has a complete love line. The beautiful young master and the handsome but ill-fated noble son stay together in the end despite the turmoil.