Bringing up past relationships
You both had lives before meeting one another. Those lives may have involved other relationships. It will be nearly impossible to tell each other about your lives, from childhood until present, without at least mentioning the existence of past partners. It’s natural to feel a little jealous when this comes up, but to become angry about it is just petty. Your partner shouldn’t have to apologize for or hide the fact that you’re not the first person he’s dated.