Extra Marital Affair

This is completely fiction and the characters of this story have no connection with real life.
People say that having an extra-marital affair is wrong, but if a person is not happy in the relationship, wakes up every day, only listens to abuses and is being physically tortured, then what is wrong in having an extra-marital affair? Is the discussion over? If she is not getting the love she wants to find in her partner, then she can look for love outside and it is not wrong to expect love from someone....
On the other hand, if a man whose wife only demands money from him, neither can she give him any physical nor mental happiness, nor does she have the strength to stand with him for the whole life, then even if such a person has a marital affair... So what is wrong? He just wants love. He has a lot of money but he is hungry for love...