
der Seitensprung
affair
A sexual or romantic affair with a person outside one's own committed relationship or marriage.
Sie hat ihm seinen Seitensprung nie ganz verziehen.
She never fully forgave him for his affair.
affair / side jump
Loading your saved state.

affair
A sexual or romantic affair with a person outside one's own committed relationship or marriage.
Sie hat ihm seinen Seitensprung nie ganz verziehen.
She never fully forgave him for his affair.

side jump
A jump performed to the side, especially in gymnastics or sports.
Beim Bodenturnen zeigte sie einen eleganten Seitensprung.
In floor gymnastics, she performed an elegant side jump.
The word consists of 'Seite' (side) and 'Sprung' (jump). It describes a jump to the side—either literally in sports or figuratively as straying from the faithful path in a relationship.
Er hat seiner Frau den Seitensprung gestanden.
He confessed the affair to his wife.
In everyday language, the figurative meaning 'Affäre' (affair) is almost always meant. The literal meaning as a jumping movement occurs almost only in specialized texts about sports, gymnastics, or dance.
Die Turnerin zeigte einen perfekten Seitensprung.
The gymnast performed a perfect side jump.
In the meaning 'Affäre' (affair), 'Seitensprung' is most commonly combined with the verb 'machen' (to do/make) or the more formal 'begehen' (to commit).
Er hat während seiner Geschäftsreise einen Seitensprung gemacht.
He had an affair during his business trip.
affair
For a relationship outside a committed partnership, both Affäre and Seitensprung may fit. Seitensprung often refers to a single or brief breach of fidelity, while Affäre usually means an ongoing secret relationship. Choose Seitensprung for a one-time slip and Affäre when the relationship lasts longer.

Er gestand seiner Partnerin einen einmaligen Seitensprung mit einer Kollegin.
He confessed to his partner that he had had a one-time affair with a female colleague.
Sie hatte über mehrere Monate eine heimliche Affäre mit einem Kollegen.
She had a secret affair with a colleague for several months.