@chai2,
Thank you all for your advice and input. I haven't seen any of your posts until now. I had already made my decision and I told her it was OK to go. I didn't want to change reading something that would make me change my mind and go back on my word. That being said
UPDATE
The party was today, I was still at work. I called her around 2:45 to discuss an unrelated topic (needed to confirm an appointment with a contractor who is doing work on our house tomorrow). She was in her car on the way to the party so she got there around 3pn. She texted me at 4:15pm and said that he had just shown up so she left the party. Then she immediately followed it with a picture of her car dashboard with the radio in view (showing the clock which read 4:18pm). It made my stomach flip a few times, but I didn't call her back and got off work at 4:30pm. I was going to use my drive home to process. At 4:45pm she called me and said she was surprised I didn't call, she had our boys in the car with her, I could hear them. She didn't say anything about this but she sounded happy and relieved that I want freaking out which would have been the case 1 year ago. I told her I didn't call her because it made my stomach flip and I wanted to use the drive home to process it before speaking to her. She said "OK, thank you. I want you to be able to do that if you need it. I'll see you when you get home.". We said I love you and hung up.
I really think this was the right thing to do. It was hard for me but in the end it was for the best. Tonight we are going to her parents' house for s'mores around the fire with the boys.
I got home from work and she told me how much she appreciated that I didn't make a big stink about it and that she recognized how hard that must have been for me and that it meant much more to her that I allowed her to go. She gave me a bunch of kisses, told me she lives me again, and we're doing good. If I had chosen the other road I can sure you we wouldn't be doing this well tonight.
Again thank you all!
Sincerely, Joe