"
For diamonds do appear to be
Just like broken glass to me
This suggests that something like diamonds which is considered by most of the population of the world to be beautiful is not to him. This implies that there are people out there who most everyone finds beautiful, but they aren't to him. He sees them as something less than ordinary. Just as he saw the flaws in diamonds by stating they are just broken glass, so too is he staying that he sees the flaws in these so called desirable people. He sees them as broken and insecure.