i’m upset over my boyfriends past

Hi everyone, a couple days ago i found out something about my boyfriend and i know it shouldn’t upset me but it really has. i’m 17 and he is 18, and i’m his first girlfriend. before meeting him i did engage in a lot of sex and hook ups which he doesn’t mind because we didn’t know each other. however, when i did meet him, all his friends and my friends that know him say he is super innocent and whatever (which he is). but i found out that at a party around 1 year ago (we didn’t know each other), some girl gave him oral sex. i know i shouldn’t be upset about this because we didn’t know each other but every time i think about it i feel so nauseas and sick to my stomach. i don’t know what to do about it because i know i cannot be mad at him but i really feel grossed out and sad by it. any advice ?