The pandemic has surprised me with both how much people are unable to just be alone for awhile, and related to this, how much they have a difficult time being with partners and family without larger social distractions.
Being able to be alone, at least in my experience, helps you to be with other people in a sincerely intimate way. People that struggle the most with their partners during the pandemic seem to be people who need socialization to distract from their own relationship problems.
If two people can be "alone together" in a room for awhile, they can still refresh, and restore their energy. This allows them to be more supportive and close when they need socialization because they aren't exhausted.
Loneliness is being forced to deal with your fear of being alone, without every taking the time to be comfortable being alone.