In need of advice..

So this may sound really dumb but I was setting up the contacts in my fiancés and I new tablet when I saw this girls name and number in his contacts already. I knew that he has had this email for awhile but this particular girl is my enemy if I ever had one. She made me feel so low about myself all throughout high school and involved herself with EVERY SINGLE MAN I've been involved with for the past five years.. My fiancé and I were dating not long before they dated our freshman year in high school (we graduated in 2015) and we dated back when we were both in seventh grade also, but as far as I know they only dated for a week before she lost her virginity to him (which broke my heart at the time) and then they split up. Well I was very upset about finding her name in his contacts because it's not the first time I've seen another girls things in his stuff. And I do understand he was with other people before we reconciled in September of last year, but the thing that makes me so upset is that I've found other girls pictures, phone numbers, I've found him trying to talk to other girls in January, but I don't see any of the things I ever gave him anywhere. It might sound so stupid but it breaks my heart that these girls still linger around while our history was seemingly wiped clean. I'm probably thinking way too deep into things but it hurts.. And out of all people it had to be her you know? 😔 I just hate being reminded of how things were, I was still loving him from afar while he was running around with lord knows how many girls and he never thought of me once. On top of that, our relationship isn't where I want it to be so there's insecurities stacked up prior to me finding her contact info. Any advice on how to look past the past? It's almost haunting sometimes but I don't want to let it get to me..