How long do you wait on a late paying client before cutting them?

Been with this client for many years. Steady work, steady pay until recently. Now they’re consistently 2-3 months behind on invoices and they keep saying it’s a temporary cash flow issue.

I don’t want to torch the relationship if it’s actually temporary. But I also don’t want to be the contractor who waits 6 months for payment because I was too patient.

How did you decide when to walk? And how do you make peace with writing off what you’re already owed?