What is the test for a spouse to prove that they are in a state of mental distress?

Cruelty must be established by proven facts and not merely by the subjective evidence and hurt feelings of an injured spouse. As Justice Denning said in Kaslefsky v. Kaslefsky [1950] 2 All E.R. 398 at page 403: If the door of cruelty was opened too wide we should soon find ourselves granting divorce for incompatibility of temperament. This is an easy path to tread, especially in undefended cases. The temptation must be resisted lest we slip into a state of affairs where the institution of marriage itself is imperilled. Human relationships are prone to ups and downs. [D.S.W.] and [D.M.W.] are very different types of individuals. Those differences point more to incompatibility than to cruelty. The matters complained of by [D.S.W.] have either not been proven looking at the evidence as a whole or I find them to be evidence of incompatibility as opposed to cruelty.