Once you married and have been with the same person, being comfortable becomes a routine in the daily life to the point where you are living as friends and not husband and wife. For the rest of your lives will be living like friends and sex once in a while. That seems the routine in a long term marriage. Reason why many people cheat. Men and women are cheating nowadays more than before because the spark of two individuals do not exist due to the routine in their daily lives. Back in the days men cheated because they would not due dirty behaviors with their wives because it was a taboo. Nowadays men cheat because women in the home are attracting their attention, which is their desire. For example, men want someone they can talk to, have rough sex, be sexy, partner, friend, someone to have fun with, sex slave, mistress, etc. That is the not including the family part.
The family part comes in another dimension, because before you reach the level of having children you need to build your stable relationship. Children grow and leave the nest once they are grown enough to find their path. Therefore if you do not build the stability prior to the having children; once they leave you are left with nothing and find your relationship bored. You start to search for some excitement you do not have in your relationship and that is where the cheating part starts and ends your marriage with your partner. Different interest start to develop and a new interest keeps you away from home.
Sex in marriage is very important to keep connected with your partner and within yourself is the intimacy that counts and sex is part of it. It does not mean that you will be having sex all day and everyday. Just have intimacy by having a conversation with your partner about anything and all.
There is instances where women have the greatest sex at home with their husband however they cheat with others because they can have a conversation about anything with the next person. It is believed that having certain conversation and lead to discussion however if depends in the level of education and/or understanding the next person may take it personal and /or feel offended by the conversation details and /or topic. For instances, some men are offended when their wives speak about the past sexual experience to the point they get jealous just hearing the details of it.