boyfriends stunning ex

how do i stop comparing my boyfriends stunning ex with myself. she is always posting great body pics of her self on her insta page which i’m sure he follows. i seem to stop sexual interaction with him because of how insecure it makes me to think of how good he has had it and his expectations would be higher than what i can give. i am a virgin and pretty sure he had a healthy relationship with her so my question is how do i get pass these insecurities and if anyone has had the same situation please give me advice