It's wrong.
Of course. For that you don't need to come here.
But I once heard [on-line] an interesting insight from a non-Jewish psychologist and author. He said that at the root of every infidelity is an infidelity of the other partner.
How so?
The classic example is when the man cheats. But it really started when the woman cheated. She didn't necessarily cheat with another man but maybe with the kids or her job. Meaning - when she put other people and tasks before her husband that is a type of infidelity.
Of course [this is me talking - not the aforementioned psychologist] there is no moral equivalent between the two. For a married person to be with someone else is immoral while spending excessive time and energy on one's children or job, even at the expense of the spousal bond, can hardly be considered immoral.
But there is something to the idea that in a solid marriage bond, people don't look elsewhere for love and excitement and both sides are responsible to make it happen. If a person's needs are not being fulfilled then they look elsewhere. [It is not the correct thing to do but that is often the reality].
I have this theory and it goes like this [you can tell me if I am wrong. I appreciate feedback. I also appreciate six figure checks with my name on them - I actually prefer that more than feedback]: Every human being has an innate desire to be loved, cherished, adored and appreciated. Most people are not focused on making us feel that way. It's not like a person goes to work in the morning and feels like everybody in the office just LOVES him. The only people we can count on for this feeling are our parents [maybe - I know many exceptions], children [not a good idea to be emotionally needy towards one's children] and our spouses.
So please: Make it the top priority in your life to make your spouse feel loved and appreciated etc. If you don't do it - then who will?? Besides Hashem [who is always Number One] there should be nobody NEARLY as important to you. That attitude will not only strengthen your marital bond but will also be very good for your children.