A person who enjoys solitude becomes less vulnerable to bad company.

Enjoying your own company changes your standards for everyone else’s. When being alone is genuinely fine, mediocre or costly company loses its main advantage, and you become far harder to keep in a situation that does not suit you. The capacity acts as a filter without any effort.

If you find yourself tolerating relationships you would not choose, look at what the alternative feels like. Working on that alternative directly, so that solitude becomes acceptable, often does more for your relationships than any amount of trying to fix them from inside.