You can tell that when Dew sits on Secondos he gives that side eye look to women and men, both human and ghouls alike to say "step back bitch, he's MINE." Or the other way around if Secondo sees someone looking at Dewdrop
Dewdrop actually shares Secondo with his personal pack of ghouls, which Dew was in. My own oc Bismuth being one of them. They were Dewdrop's first pack on earth when Secondo summoned him, and Dew came to love and adore them dearly.
However, @puppercupboard, who I plot all this out with, puts it best with "they are not a 'step back bitch, he's Mine' couple, they're a 'good, keep looking, we both know you wish you were me ♡' couple."