found bite mark on bf ?

long story short i found a bite mark on my bf's right shoulder..i've never seen it before maybe i just never paid attention but he says it's a scar from his ex gf from sex so i'm guessing (praying) its old? he seemed pretty honest and straight forward with me when i confronted him but now it's all i'm thinking about and i'm just super emotional and needed to vent i guess..any advice?