Did John Wesley use to pray in Latin due to the bad relationship with his wife? In his book, The Attributes of God, A. W. Tozer mentions that John Wesley had a bad relation with his wife and because of this failed marriage, it is said that he (sometimes) used to pray in Latin so that his wife won't understand what he was praying about.
The version of the book I have has no bibliography, so I am looking for the primary source of these affirmations.

Some men have wives that are wildcats—difficult to get along with—and they think they are tempted above all others. John Wesley was married to a wildcat, and she didn’t even have her claws trimmed. But God got John Wesley through all right.
He used to kneel down and pray in Latin so his wife wouldn’t be able to know what he was saying. And while he prayed, she threw old shoes at his head! Not a very nice family affair, but that’s the way they got on.
The time came when Wesley said good-bye to his wife and went off preaching, even though she didn’t want him to. And they never did get together much after that, though he saw to it that she was taken care of.
She stayed home and grumbled as he went out everywhere preaching the gospel and transforming England. Then one day he was riding along on his horse, meditating or praying, looking up in the sky. Someone rode up alongside him and said, “Mr. Wesley, your wife is dead.” And he looked down and said, “Oh, she died, did she?” And he went back to looking up. Wesley got along all right, in spite of the wife he had.
https://www.worldevangelismcenter.org/john-wesleys-wife/
and http://www.worldevangelism.net/john-wesleys-wife/

What is the source of the idea that John Wesley used to pray in Latin so that his spouse won't understand?
From the Wikipedia article on the subject:

Though Wesley favoured celibacy rather than marital bond, he married very unhappily at the age of 48 to a widow, Mary Vazeille, described as &quot;a well-to-do widow and mother of four children.&quot; The couple had no children. Vazeille left him 15 years later. John Singleton writes:

&quot;By 1758 she had left him – unable to cope, it is said, with the competition for his time and devotion presented by the ever-burgeoning Methodist movement. Molly, as she was known, was to return and leave him again on several occasions before their final separation.&quot;

Wesley wryly reported in his journal, &quot;I did not forsake her, I did not dismiss her, I will not recall her.&quot;



What is the source of the idea that John Wesley used to pray in Latin so that his spouse won't understand?

Most likely from the author's personal sense of humor (the entire presentation seems to adopt a colloquial rather than scholarly tone); Latin basically served as an international and prestige language in much of the Western world until the late nineteenth and early twentieth century; it's highly unlikely that its usage in either individual prayer, private conversation, or public discourse, was done for the purpose of hiding anything from anyone; many Catholics, with which High Church Anglicanism is intimately connected (see Anglo-Catholicism), still serve Mass in Latin even today, let alone in Wesley's time.