Designing the confining situation
The forced proximity situation needs internal logic that survives scrutiny. Start by identifying what makes it genuinely inescapable for these specific characters: not just the external constraint (the blizzard, the shared apartment), but the personal circumstances that make escape impossible or too costly. A character who could check into a hotel but cannot afford it, who could call a friend but has burned that bridge, who could quit but cannot lose this job — the confinement is always partly external and partly the character's own accumulated circumstances. The most durable forced proximity setups are those where both characters have specific, independent reasons why they cannot leave, so the reader cannot simply route them out of the problem.