but I acknowledge that there is an objective scale of attractiveness

Okay, I'm gonna stop you there. Brittany Spears is a two on a bad day and a ten on a good day. That shit is completely subjective. Some people think Adele is hot and some people think she's not. It has 100% to do with how you're styled, how you present yourself and the vibe you exude. People are pretty in pictures some days and ugly on others and all that matters is that your partner thinks your beautiful.

With that said, I would say my boyfriend and I are on the same level of attractiveness, which would be a 6 to 7 on a scale of 10

So like I said, the issue here isn't whether for not really are equally attractive, because honestly if you're both not deformed then there's no such thing. The issue is that he doesn't think you're equally attractive. He thinks you are an odd couple, and he thinks your friends won't like you.

The title of this post is "he won't introduce me to my friends" but it should have been called "my boyfriend doesn't think I'm attractive".

Life is too short OP! Somewhere out there is a guy that will go to the grave telling you he can't believe how lucky he is you even give him the time of day.