Moving on from a finished relationship can be difficult enough on its own, but when you discover that your ex-boyfriend has a new girlfriend, it can drive you to distraction. In order to cope with this occurrence when it crops up in your life, you need to tend to your own emotions while making it possible to handle the situation with maturity in social settings.
Keep some distance between yourself and the new couple. As much as possible, avoid being in shared social situations where you will see him with her. To some extent, they will be more out of your mind if they are out of sight and you won't have to see as much of what their relationship is like.
Resist the temptation to find out more about her. If you find that you're comparing yourself to the new girlfriend, you may find yourself wanting to know more about her and thinking about doing things like looking her up on social networking sites or asking around your social circle for details. Remember, however, that even though you might satisfy your curiosity, you're unlikely to find out anything that's going to make you feel better about the situation.
Limit the amount of time you spend thinking and worrying about the issue. You need to give yourself some time to process and recognize your feelings as well as talk through them with friends, but stop yourself whenever it gets to be too much. If you're starting to feel overwhelmed, repeating yourself or being physically affected by negative emotions, it's time to take a step back.
Distract yourself. Give yourself lots of constructive and/or enjoyable things to do to keep you busy and your mind occupied. Make plans with friends as much as possible, as they can help keep you from dwelling on the issue or complaining more than is healthy.
Do what it takes to make a good showing at any shared social events. If you have to attend professional or social gatherings with the new couple, strive to be as courteous and mature as you possibly can. While these situations will still be difficult, you will feel much better afterwords knowing that you handled them well.