infidelity in relationship is not only applicable to women,men are also involved but since the question is basically reffering to women,men will be less mentioned.
women cheat bcause of so many reasons. i will start by saying why most women cheat is because they are sensually created to be sexually active even more than men.This fact affects any woman that cannot control her urge. most men handle their women on bed just to satisfy their own urge. you will agree with me that women can stay longer in sex than men so in a situation where men constantly isnt satisfying the women,she tends to seek satisfaction elsewhere eventhough she loves her man.
Also when a woman feels lonely, she might want to seek emotional connection. in so doing she ends up having sexual affair with another man
No extral marital affair will not involve sex and the main thing that lure women into it is seeking solace outside because of one reason or the other.