A stationary store might seem like an unlikely place to find love. But Bob Slate is where self-described “pen addict” Laura Donohue spent her Harvard undergrad days in the early ’80s, lusting after cards and swooning over school supplies. Donohue became a loyal customer — and she wasn’t the only one. Last March, she stopped by the Mass. Ave. spot for a new Cross pen, only to be confronted by crying patrons who were dismayed that the shop, which opened its doors in 1933, would be closing.