Why do people stay in relationships when they get cheated on?

For some it can come for insecurity, disbelief, etc. I know when I first stayed longer than I should have after the affair, it was because I was in such shock. I never would have ever guessed he would do that to me. I was so in love with him I had done everything he ever asked and more. I was honest, patient and loyal and loving. I thought maybe there was something else, and all he needed was forgiveness to repair and do better going forward. Not to mention having to cancel all future plans with someone you dreamed them with is both scary and devastating. Some want to save it even though normally at that point it is already lost. Most things that seem black and white from the outside feel so gray once you are the one wrapped up in it all.

From the experiences I've come across, self-esteem plays a part.

Forgiveness.

They forgive, and the partner regrets.