Husband Facebook searching ex through our 6yr relationship

I live with resentment towards my husband. We’ve been together for six years. I found out he’d been Facebook searching his ex wife and the ex before me. More so his ex before me through our entire 6 year relationship. He’d bring the girl before me up casually throughout our relationship before and would get defensive when I told him it bothered me. He’d still do it when trying to tell a random story where he didn’t need to bring her name up but he’d do it anyway. She’s the one that left him. They were in a 4 year relationship and two of the later years they slept in separate rooms. He swears he has no interest in her but after finding out for myself he’d search for her on Facebook at least 2 times a week for 6 years, well everything went sour for me. I found this out last August and I’m still very salty. He swore he’d stop. I feel fooled into thinking he was all about me. I worry I’ve been a rebound for 6 years. I worry somewhere in his head he’s lied to me and himself about moving on. We never settled it. And I want to bring it up and talk about it but I don’t know how to without coming off completely bitter. He’s a master at distracting me from the subject at hand. That’s why I never got closure the first time i brought this to his attention. I now see him as being disengenuous throughout our relationship. Is it normal for him to do that? Is it not normal for me to feel this way now?