When someone has wronged you, it's only natural to feel angry and upset. Figuring out how to set those feeling aside and interact with that person is an important social skill, especially if you have to see her regularly. The more relaxed and cordial you are when you see her, the smoother things will go. To keep conflict to a minimum, remember to work on forgiveness, plan conversational topics in advance, keep relaxed and remain polite at all times.
Take a deep breath or two before you have to be around the person you're upset with. If you notice yourself tensing your muscles, take a moment to relax and stretch. Studies have shown that anxiety increases muscle tension and heart rate. The more you can relax your body, the more likely you are to reduce these symptoms and feel at ease.
Prepare a mental list of talking-points and safe-subjects to discuss, just in case you get stuck in long conversation with her. That way if emotions produce an awkward lull in conversation, you can keep things moving.
Engage with him for as long as politeness requires, no more and no less. Running off will seem rude, and spending more time talking than necessary increases the opportunity for discomfort. Mentally prepare to spend at least a few minutes exchanging pleasantries.
Look at the person between her eyes if making eye contact is uncomfortable. Looking away from her face, or at her shoes, can appear evasive and rude.
Speak as close to your normal tone of voice as possible. Try to remove any hostility from your tone and watch for sarcasm. Avoid trying to sound more enthusiastic or cheerful than you feel, which often sounds fake. If you cannot control your emotions well enough to converse in depth, stick to smiles, nods and general comments. Ask leading questions that allow him to carry on the bulk of the conversation.
Remove yourself from the conversation as soon as socially acceptable. A good way to do this is to draw a neutral third person into the conversation shortly before your exit. This will occupy the person you're upset with and distract her from pursuing further conversation. Say something like, "Emma, have you met Claire? I had no idea you two both went to the same high school." As soon as "Emma" and "Claire" begin chatting, excuse yourself on some pretext and do not return. If there is no one you can draw into the conversation, politely excuse yourself to perform a task that involves leaving the room.
Focus on healing from your hurt so that interactions with him become less distressing. Try meditation, exercise, therapy or simply talking to friends. Avoid dwelling on negative feelings or creating more drama by indulging in destructive impulses, such as bad-mouthing him to others.