I find it hard to believe that you just now found out your performance schedules. For the record, two of them have been posted since this time last year and the other would have been listed in the group's contract you signed in August.
And if you can't keep track of your rehearsal schedule, maybe it's time to pare it down a little. That's not admitting defeat, it's being smart. You are no good to ANYONE if you can't make it to your commitments on time and prepared.
So now it has come time for a "Come to Jesus" talk, as my mother likes to call them. You are an adult. Your decisions should be your own and you should be old enough that your decisions should be sound ones. You will decide what is important to you and you will realize your limitations and you will commit yourself where it is most prudent.
Or I will do it for you.
No love, once your friend but now your boss with a rapidly failing temper and one hand on the 'fire' button,