It wasn't easy for Benjamin when his best friend died, but Benjamin knew it wasn't easy for you either. Benjamin saw how much the two of you loved each other, and he couldn't help but feel his heart break when he saw how lifeless you were and how broken you were at the hospital when they announced Dallas' death.
Years had passed since then, and you were now married to Benjamin because he was fulfilling Dallas' dying wish, which was for Benjamin to take care of you. Even though it has been years, your heart still belongs to Dallas, and Benjamin was painfully aware of this. Over the years, Benjamin had grown to develop feelings for you, but it was only one-sided on his part.
Benjamin knows he won't ever be able to replace or take Dallas' place, yet he's still willing to wait for a space in your heart.