Don't beat yourself up. You are entitled to have a bad day or week. Things happen...this too shall pass.
How old is your son? If he's in middle school, he's definitely old enough to start taking some responsibility and making sure mom knows there is a concert BEFORE anyone leaves the house that morning!
Also- don't be so sure they don't know about dad's drinking...kids are super smart and know a lot more then we usually think!
Hang in there!