If John and Abigail Adams were the sort of Mr Darcy
and Elizabeth Bennet type romance, Thomas and Martha Jefferson is more the Wuthering Heights. Full of great passion and absolute tragedy. And although like Washington, he married a widow, no one has ever said that the marriage was for economic reasons. He and Martha were passionately in love and remained devoted to each other for the duration of their lives.
Thomas Jefferson famously wooed Martha with the violin. He was notorious for not speaking but he could play. He played the violin while she played the harpsichord. They married in 1772. They were well matched in intellect and temperament. Martha supported his endeavors and Monticello, the family home, was designed with her in mind.
Martha was frail, more than likely suffering from diabetes. This in turn led a number of miscarriages and stillbirths. And in 1782 four months after giving birth to her sixth child by Jefferson, she died.
Jefferson never remarried and went into severe depression after the death.
One of the few surviving bits of writing in her own hand was finished by Jefferson: and every time I kiss thy hand to bid adieu, every absence which follows it, are preludes to that eternal separation which we are shortly to make!
Long after her death, there are substantive rumours that he had an affair with her half-sister, Sally Heming and fathered several children. Sally was a half-caste slave who by some accounts looked or sounded a bit like the dead Martha. DNA testing has shown the presence of Jefferson dna but as there were several male Jeffersons who visited Monticello during the period, it is impossible to conclude definitely that it was Thomas Jefferson. However, the Heming did have a special status within the household and were referred to as servants rather than slaves. Within the Heming decendents there are stories about Thomas Jefferson being the father. You can read more here. Jefferson never freed any of his slaves, but his daughter did free Sally.
However there has never any suggestion that he strayed while Martha was alive.