In love, this Mercury tends to speak more quietly than it thinks and to remember more than it ever says. I often notice that people with Mercury in Cancer pick a partner by voice and by the way they hold a conversation. The timbre, the pauses, the willingness to hear a thing out to the end matter more than looks or a list of achievements. The first serious impression usually forms in one long late-night talk, and afterwards it's remarkably hard to dislodge with mere new facts.
Inside a relationship, this person tends to talk in roundabout terms. They'll rarely say "that hurt" outright; more often they go quiet, or start telling a story about someone else's acquaintance in which the partner is supposed to recognise themselves. The habit builds a thin but dense layer of the unsaid, and over time it settles like sediment. A blunt partner reads as rough, a rough one reads as dangerous, and the circle of people who feel safe tends to narrow.
Memory works both against every conflict and in favour of every warm moment at once. They remember which mug the partner likes in the morning, and they remember the line that wounded them three years ago at someone else's wedding. Making peace tends to come easily; the scar tends to stay. None of this is fixed in stone — it's a pattern worth noticing in yourself, not a script you're bound to follow.
In my experience these relationships come into their own when both people agree on a simple formula for asking plainly, and on the right to say "I'm not okay right now, no explanation needed". Then the softness stops being a way to avoid the conversation and becomes what it was meant to be in the first place — a warmth that can hold a partnership together for years.