Need advice lies

Relationship advice, my partner of 7 years has been telling lots of lies our whole relationship ive been able to get over some, but today I find out another lie and I want to know if I’m overreacting... hes always told me I was his first in every kind of way (we were 17 when we met) today I find out he lied about that! 7 years he’s been telling me this me believing him, I don’t care if their was someone before me it’s the lie that hurts, am I overreacting? Please help 😩