Is it normal to masturbate to my gf pics?

so me and my gf have been on a break for a month or 2 and not been sexually active since then so it got to the point where i found some unintended "flattering" pics of her for some visual aid. One way or another she found out about id rather not go into detail, but she was pissed and creeped out by it. It started a big fight and i she asked if id done this to other girls pics i was honest with her and told her i used to do it to do it to girls i went to school with pics when i was 14 to like 16 and she became digusted with me, im 21 now and hers were the only ones iv done it to in years but shes still creeped out and thinks im disgusting and a pervert for what i did when i was a kid. I tryed telling her that its normal and most guys going through puberty do similar things but she still insists im a freak and allowing this to flush our 1 year relationship down the drain. So is she right am i a freak for what i did? I told her i wouldnt do it again and i wont but she doesnt trust me so what can i do to pull my relationship from the ashes? this girl really means alot to me.