Learn yourself well enough that loneliness cannot negotiate your standards.

Loneliness is an effective negotiator. It argues for lowering your standards, accepting less, staying somewhere that is not good for you, and its arguments are persuasive because the discomfort is real. What holds against it is knowing yourself well enough to recognise when the negotiation has started.

Decide your standards while you are not lonely and write them down. Then, when the feeling arrives, you are consulting a decision rather than making one under pressure. The loneliness still has to be lived through, and it does not get to set the terms.