My ex became "friends" with a woman when he was overseas. Yeah. Friends. We are getting a divorce and he has lost a wonderful woman. Me. And while she has repeatedly BEGGED him to choose her, he won't because that "relationship" destroyed all that was precious to him. He lost his family and that cannot be replaced. It can be added to, but never replaced.
You can't really help who you fall for, but you can prevent putting yourself in a situation that will create opportunity to "fall." No one wins when cheating occurs. You won't wind up with him. He might seem great and wonderful and all that, but he won't choose you over his family. If he did, would you really want him? If he does choose you, he is SO not worth your time, especially if he has kids and walks away from them for you.
We all make errors in judgement from time to time, especially where urges are involved. But the true test of our character is in how we handle the challenges we face.