During the three years of their separation, he still felt a deep love for her. Although he didn't think his love was any less than the Young Master's, it became apparent to him when he saw Joshua Sulliven repeatedly taking sleeping pills to fall asleep, when he witnessed him calling out her name in a drunken stupor, when he observed his cold and irascible demeanor, as if his heart had turned to ash, and when he saw him living listlessly as though waiting for death.
At that time, he suddenly realized.
Perhaps the act of loving someone cannot be measured in terms of more or less, nor is there such a thing as deeper or shallower affection. It's just that some people are fragile in love while others are driven mad by it.
He suddenly understood that without Keira Leaf, he could still go on living with the memories of her and him, but without her, Joshua would die, or live a life worse than death.