The announcement of your ex's plans to remarry is likely as uncomfortable and fraught with mixed feelings for your ex as it is for you.  While the news may come as a surprise, do not make negative comments or ask intrusive questions. Thank your ex-spouse for letting you know and leave it at that. Remember, the two of you are no longer in a relationship and, unless you have kids, your ex is not obligated to keep you informed about his or her personal life. It is a sign of healthy trust between you that your ex has told you the news.  Be sure that you don't make a comment (or even a surprised or confused facial expression) that could compromise the relationship you have built. It is customary to celebrate the news of a friend or family member's engagement, so why should it be different because it is your ex-spouse?   If you have an amicable relationship, or especially if you have children together, it might help to get the new marriage relationship off on the right foot if you pick out a simple card of congratulations, and simply write "Wishing you all the best!" Or consider a small gift, like a bottle of wine or a gift basket for their new home. Heartfelt congratulations means a lot. If you do not have a good relationship with your ex, or if you think the new spouse is the type who would become jealous, you might skip a card or gift. Rather than badmouthing the new marriage or new spouse, focus your attention on more positive things in your life.  It is healthy and right that your ex should find love and remarry. Even if you have not yet moved on, your spouse has a right to move forward with life. You should also avoid making negative comments about your ex in front of your children, if you have them. Research shows that children who have positive, healthy relationships with both parents after a divorce have higher wellbeing than kids whose parents don’t get along. Sometimes relationships with exes are not healthy, and one person may try to use situations like this to emotionally manipulate the other. It is not unheard of for exes to make comments about how much better the new spouse is at fulfilling his or her needs, or how much better the new spouse looks, or cooks, or listens, etc.  If you find yourself feeling as if your ex-spouse is purposely rubbing the new marriage in your face or reveling in how miserable he or she thinks the new marriage makes you feel, remind yourself of how childish that is of him or her. In fact, it is a sign of immaturity and an inability on your spouse's part to let go of past hurts between the two of you. Be the bigger person by wishing your ex the best and doing your best to not revisit the topic. If your ex insists on discussing the new marriage or making comparisons, ask politely that he or she stop, and if nothing changes, you may have to reconsider future contact with this person. In situations where you must communicate for the sake of children you share with your ex, counseling may be the only option. If you find yourself getting flustered, take a break and give yourself a little pep talk. Try using some reassurance statements, such as “This is upsetting, but I know how to deal with it” or “I don’t need to get into an argument about this.” You can also try some “relaxation reminders,” such as telling yourself “Remember to take a deep breath and relax” or “I can stay calm through this.” Focus on your own life, not your ex-spouse and his new spouse. There are few relationships more intimate than the marriage relationship, so it is natural that you would have ambivalent feelings about the new marriage and spouse.  Do not make little issues into bigger ones just because of your ill feelings about your ex-spouse's new wife or husband. There are so many wonderful things you can think about and do rather than focus on negative feelings about your ex-spouse's new marriage.

Summary:
Congratulate your ex-spouse when he or she tells you the news. Consider sending a card or buying a small gift. Avoid making negative comments to your ex. Ignore any attempts by your ex to push your buttons. Keep things in perspective.