My boyfriend’s ex girlfriend

I’m jealous of my boyfriends ex girlfriend. He is the kindest sweetest most caring man and does everything to make me happy...we have so much fun together. But... sometimes we will be doing things and he will mention his ex girlfriend. I never say anything when he mentions her but i think he can tell it bothers me. He apologizes right away every time and it’s not that I’m mad that he still thinks about her, I’m just jealous.