Irish, I'm very sorry that you had to see the two of them holding hands, etc., but you actually got to see her and now the "cute, lovely woman" is out in the open. They are always different and many of them do look older or just not the type our spouses would have chosen had they been in their right minds.
You will always hold some feelings for your xh, but those feelings will not be the same as the ones you had when you were in love w/him. It takes a long time for those feelings to change and it will be done gradually and one day, you'll be surprised how those feelings have changed. Give yourself some time, the wound is still very raw and open.
I am glad to see that you had your family around you last evening. How was your son's prom? Did he enjoy himself? What about you? What are your plans for the week ahead?
Irish, please take care of yourself. No one can hold a candle to you. Just remember, you are a unique and very special lady.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
