Sorry to post another Prudence letter but this one was just too good...
Is It Time To Get Over It?:
When my ex and I were married, we had trouble conceiving and years of heartache. I thought our marriage was strong enough to survive this, then I discovered he was having an affair with my sister. We had a huge, traumatic confrontation and my then husband and I decided to move and make a fresh start. A few weeks after we moved, my sister gave the news that—surprise!—she was pregnant. My ex then divorced me to start a family with her. Because I'd just started a new job and had a mortgage, it was financially impossible for me to leave. I stayed in the new city by myself and eventually made friends and settled there. My parents were also very hurt and angry, but when the baby came they mellowed and reconciled. My niece is now 5 and I have never met her. We take turns attending family functions because I can't bear to be in the same room as them. Recently my parents gently asked if I would consider having a Christmas dinner with my sister. I told them I would think about it and I really did. I took a deep breath and went on my sister's Facebook page for the first time. There, I saw hundreds of happy pictures of them as a family. My ex-husband kissing her after she'd just given birth, photos of the happy first birthday party, family trips, etc. She was tagged in a status update from my ex: "Celebrating another amazing anniversary with my beautiful wife, thank you for giving me so much happiness and our perfect daughter." I literally vomited after reading that. After five years, is it time for me to get over it and try to force myself to at least tolerate their company?
It's no wonder what you saw made you sick to your stomach. The violation against you was enormous. However, I don't think you should conclude that the only way you could be with them is to have a bunch of air-sickness bags with you. You have been in a bubble of denial for the past five years, so a tidal wave of evidence of the happy family life you feel these cheaters stole from you is bound to be overwhelming. If over the past few years you'd had some minimal contact with them and knew your niece slightly, you would be in a different place emotionally now. Yes, you might have still concluded you want nothing to do with them, but you would have made that decision from a more rational place. So give yourself time. You may want, possibly with the help of a therapist or even a friend, to give yourself some desensitization therapy. Instead of consuming pictures of the past five years at one gulp, over the next few months you could look occasionally at pictures of your niece. She is the innocent party here, and focusing on her might enable you to see that painful as it is, something positive has come out of all this. But Christmas is too soon for this. If you are going to find yourself being able to be in the room with this reconstituted family, it would be better to do it at a less loaded time—say a weekend in February with no connotations of holiday joy. Whatever you decide vis-a-vis your sister, be proud that you have moved on and built a happy life for yourself. (And how often do brothers- and sisters-in-law get it on? Just a few weeks ago I got a letter from a woman whose fiancé impregnated his brother's wife, but the brother remains none the wiser.)