Apologizing to an old affair

So I did it. I’m 27 F and my bf 29. I’m dating someone I really love and I invaded his privacy by going through his phone a little. I’m upset bc I saw that he reached out to a woman who SA him in the past.

He reached to apologize and said “sorry I was too much of a coward to leave Gabby (his ex).. I didn’t mean to lead u on.” The wording may be a little different, “want to lead you on”.

Honestly I kinda wanna go back and finish reading but as a partner I feel disrespected. She recently came into town and so did several common friends that they have together from the group. He was pretty upset he wasn’t able to hang out with them and I told him at the end he could’ve but kind of uncomfortable to know ur old situationship is there too. Idk if I was invited or not but I wasn’t prepared to meet her.

How do I approach this?