my girlfriend left me and within 1 week she went to a guys house who invited her over from instagram. She had never met him before, he literallly just messaged her saying come over for sex and she did.

I feel so shit about myself. Was i not good enough sexually?? did i not fuck her well enough? This has ruined my self esteem for months. How do I recover from this?

Each day i try and tell myself to accept it but it just eats me up inside. Was i not good enough for her?