This issue isn't near as black and white as others are making it out to be.

1) Unless you're chris hemsworth it's unlikely that you'll ever be the hottest guy a girl has ever been with, but that doesn't mean you're trash. You probably also don't have the biggest dick, or make the most money, etc, etc. At least on single vector analysis there's likely to have been a past partner who outpaced you.

2) What actually matters is how your partner treats you on a daily basis. Do you guys always want to fuck? Is she excited when you come home? Does she enjoy telling her friends the cool things you do for her, or interesting parts of your life / career? Does she want people in her life to meet you? Is she proud of you?

By the way these things are influenced by both attractiveness as a partner (not just physical, but cumulative) and also health of the relationship.

So, this crushing feeling, if it's just your ego then get over it, but if the feeling is because you've now connected the dots and realize retroactively that your partner treats you like garbage then that's a different story.