Did I overreact? Prob with GF?

Really this could go two ways. 1. She could be just wearing them because she wants to be an independant woman and wont always be bossed around. OR 2. She might be using you to make her ex angry because he cheated on her and she wants to make sure he knows what she is doing and that she is going to wear his shirts so he knows its pointed at him. I mean i dont know the girl or you. But if she is wearing and representing another man, you might want to sit her down and tell her it hurts you and that you dont want her to always representing another man. Or buy her a new shirt. I mean take a good look at how she reacts around you or when she sees the ex. Hope i could help.