How important is fidelity in a relationship?

For most women, fidelity is the most  important thing in a relationship. If their partner having a sex relation with another person, It destroys the feeling from the another person from  the another person and also the confidence is lost.
The culture and the tradition in which the people live plays a big role because in some culteres it is somthing normal to have two or three wifes. For example like in India our Arabic speaking countries.
But for some women, emotional cheating is more devastating than ‘having sex with another people'.
That my partner has sex with another person, would bother me a lot because I believe that if he has gone to look outside, it is because I do not give to him what he need.
Therefore I could not forgive an infidelity, or if I forgive her I wouldn't forget what happened and that would not let me be with that person. Everyone says we deserve another opportunity and I agree but for me infidelity is a concept that costs me much to assimilate and forgive.
It’s a wound that is far difficult to heal than its physical counterpart. If you’re in a relationship, you want your girlfriend our boyfriend becomes only for you.
I also have to keep in mind that I was never fall in love so I do not know what I could do if I fall in love. I do not know if I would give a chance to a person who has been unfaithful to me.