It is wrong to have an affair but the degree of guilt one should feel is based on different factors. Murder can change to manslaughter and even self defense at times as well as affairs of the heart can also be considered at such levels. Here (below) are some of the points one should could consider before judgement is passed.
(1) RELATIONSHIP- If someone is in a relationship where expressions of love have stopped for a considerable amount of time and that has been noted to a partner, well then extra- curricular activities can seem a bit more reasonable.
(2) OPPORTUNITIES- Rock Stars, Entertainers etc have people throw themselves at them and when things at home aren’t just right they appear right just in front of their eyes and hands. In other words those who actively search for an affair on a website or late night bar are more at fault then when it’s thrown in their face.
(3) BORED- The degree of boredom one finds with a partner and if they express such emotions should also be taken note of in the guilt factor.
(4) ABUSE- Physical & emotional abuse by a partner on a regular basis can lead one to seek love and support from another’s arms. Of course physical abuse should be a reason to leave a relationship as a whole but sometimes a partner might find it difficult at the moment to jump to another shore.
In the end unless I’m sleeping under the bed who am I to judge why someone commits this act(s) of disloyalty. It’s up to them and their relationship with said individual as well as G-D.