Affairs, whether emotional or physical, can be devastating to a relationship. They can seriously affect the trust in your relationship and this can sometimes feel too difficult to rebuild without the help of an impartial, experienced couples therapist.
A couples therapist will help you to understand any underlying reasons for the affair, and to work through any issues that need to be addressed.
Esther Perel, a leading relationship psychologist, has given an interesting TED Talk on Infideility, which you may find helpful to watch:-