Don’t trust boyfriend please help

So tonight I went in my boyfriends work bag to get something out, and I found this stone heart. I questioned him about it and he told me he had given it to his ex girlfriend. I asked him why it was in his bag and he told me it was because he likes stones?!?!?!? He does like ornament stones or whatever, but I’m just finding this weird? He doesn’t get why I’m angry but am I being petty. Why on earth would he keep this in his bag?!

I just don’t get why he’s decided to keep it in his bag that he carry’s with him at all times?