Am I Overreacting?

So...I just found at that my boyfriend's ex wife stopped by his house tonight to "borrow his phone charger" even though their phones don't take the same charger and she knows that. He didn't tell me until after she had already came and gone. I'm pissed that he thinks it's okay for her to casually stop by to borrow his stuff. It's not his job to supply her with things. Am I over reacting or is it okay for me to be upset?