I would feel betrayed too and I would mention to your brother that you are quite hurt by this and how would he feel if it were the other way around.
You still have the worries and irritations and unfortunately when you have children they dont go away.
You have a right to be annoyed, it is not petty it is downright hurtful.
Mention it to your brother, definately. It is disloyal to you. FULL STOP !!!!
Take care and calm down with a bottle of wine tonight (preferably out of any money you get for maintenance!).
I am on your side on this one.
Take Care
katie.
xx