Treat her ex the way you want to be treated in every respect. You can’t control his behavior, but you can control yours, so take the high road whenever possible, says Munroe. If they had kids together, you'll obviously interact with him more often than if they did not. In such cases, Munroe suggests letting your wife's ex help determine how you relate to each other. For example, if he doesn’t seem to mind that you are a part of her life, don’t make a big deal of it either. Be friendly and work together to create a friendly relationship when you come in contact with each other. If he blames you for the break-up or treats you with animosity, avoid him as much as possible to prevent his anger from becoming yours.

Remind yourself that your wife has chosen to be with you now and not him, suggests Diane Gottsman, an etiquette expert and the owner of The Protocol School of Texas, writing for "Hitched." Don’t allow his words or the words of your wife's family members to make you feel unworthy or insecure. Smile and remember that his time was then and your time is now. Take the opportunity to work to make your marriage the best it can be without concern for how he did things or how friendly they are when they are together. Remember that nothing positive comes when they are at odds, especially if they have children together, so accept that a friendly relationship is desirable because it reduces the friction that could creep into your own relationship if they fight all the time.

Don't put any step kids in the middle of conflicts over the ex's behavior. Any such conflict is often best handled by your wife. You can listen carefully, affirm your step kids' feelings and refuse to take sides, suggests Munroe. If the kids tell you that he's saying mean things about you, Gottsman recommends refusing to respond in kind. Instead, she suggests explaining that they know what is true and what is not. You can also suggest to your wife that the kids could benefit from a counselor or someone with an objective viewpoint.