I was reading your post and felt like I could have written that myself. It was comforting to know that someone else out there is feeling the same way. I have quit drinking and loved it but for whatever reason has always gone back to drinking for long periods.
I too am thinking about a graduation party that I am kind of afraid to go to because I know people will be drinking there and I cannot. I am going to have my boyfriend there because of that and will tell him to make sure that I do no drink. Maybe you could enlist the help of a friend to do the same for your son's birthday party.
Maybe we can keep in touch and help each other when we feel the urge since we are kind of in the same boat. Not sure your family situation, but I am a single mother with 3 boys (15, 14, and 11). It's up to you. I just started this journey myself and looking for motivation and realizing just how much I have been rationalizing with myself about "just one drink" or "just one night" even though I know it's not true.
I wish you luck and strength!