I used to think I could never stay if a man cheated on me but that changed once I got married. I am not 100% sure I would stay, but I cannot say 100% that I would automatically leave.
If I were dating someone, trust me, I would NOT stay. Real life has not even hit your relationship and there is infidelity? No thanks.
There IS a cost (emotional, social, financial, spiritual etc) associated to divorce and so it really depends on the couple and the circumstances that led to the infidelity and of course whether it is something you can truly get over. If you have been married for over 10 years, getting divorced is not just the end of a relationship. It is a redefinition of your family, your life as you know it. If you have children, you have to face the possibility of someone else raising your kids. No ma'am. I may be unhappy in a home with a man who cheated on me and we can be civil to each other especially in front of the kids, I told DH I am not going anywhere! It may mean I remain celibate and don't date but I will get to be in my kids' lives 100% and choose who gets to be in that home with them.
Some people cheat because it's a character flaw. It is 100% a part of who they are. The person does not value commitment, does not respect other people and is plain incapable of being faithful. That is they type of person you leave, even if you are married.
Other people cheat, a one-time thing because they made a poor decision at just the right time. I think it is naive to think you or your husband can never be unfaithful. Anyone can, and it is a matter of keeping your marriage strong and making good choices. You have to be proactive. Of course, choose the right person, who is faithful and has values, then nurture the relationship. Don't go pouring your soul to people of the opposite sex. Don't go out getting drunk with people of the opposite sex. Do not seek fulfillment with someone else at a time when your relationship is struggling - even for innocent things. Affairs like these, it is possible for a marriage to recover. Not always, but it can.
Watch this TED talk:
http://www.ted.com/talks/esther_per...as_ever_loved/transcript?language=en#t-662528
"The vast majority of people that I actually work with are not at all chronic philanderers. They are often people who are deeply monogamous in their beliefs, and at least for their partner. But they find themselves in a conflict between their values and their behavior. They often are people who have actually been faithful for decades, but one day they cross a line that they never thought they would cross, and at the risk of losing everything. But for a glimmer of what? Affairs are an act of betrayal, and they are also an expression of longing and loss. At the heart of an affair, you will often find a longing and a yearning for an emotional connection, for novelty, for freedom, for autonomy, for sexual intensity, a wish to recapture lost parts of ourselves or an attempt to bring back vitality in the face of loss and tragedy."
You often hear of couples who were doing fine until they lost a child, parent, baby, job and then someone cheats. I don't know if I could get over an affair but I would try it depending on the circumstances. Of course if I cannot forgive him then it's a wrap.