Hi there,
I've been sober just 1.5 years. My 40th birthday was planned and tickets bought for a beer fest at night in a museum prior to my quit. It was a group of us turning 40.
Here's what I did: I gave my ticket away. I didn't go to my own 40th birthday party. I may not be as close to my crew as you are with yours but my husband told them I was sober. He still went with my brother in law for the others. I'm 1.5 years sober now. Starting off the 40s good here. I don't regret it. I don't miss that one night at all.
I might have regretted acting like a drunk ASS like I'm prone to doing. Instead I think I read on here, watched TV, got some rest and was up and at em the next morning. It's much better. You'll have other activities with them later, or perhaps you're be more used to being sober by next year.