The hardest part of this pairing is that both of them can go quiet instead of saying what actually hurt them, and then wait for the other to notice. Cancer retreats into the shell and hopes to be coaxed out. Scorpio goes still and watchful, deciding whether trust has been broken, and won't say so until much later, if at all. Put them in an argument about something small, like Cancer feeling brushed off when Scorpio cancels plans for the third time to deal with work, and you get two people convinced the other already knows what's wrong, both wounded, neither talking. That silence can sit in a room for days.
But underneath that stubbornness is where this pairing actually earns its reputation as one of the deepest in the zodiac. Both are water signs, which means neither has to explain why they cried at something small, or why they need to check in twice a day when the other seems distant. There is no translation required between them, no convincing the other that feelings are relevant data. Cancer's Moon-ruled instinct to nurture meets Scorpio's Pluto-driven hunger for total honesty, and together they build a bond with almost no polite distance left in it. Cancer will remember the exact way Scorpio takes their coffee. Scorpio will notice the one text Cancer didn't answer and ask about it directly, which Cancer secretly craves even when it stings.
What makes this work long term is patience with the withdrawal, and enough courage from both to be the one who knocks on the shell first, or breaks the stillness. Neither owes the other an easy read. They just have to keep choosing to show up.