Although I am not a psychologist/psychiatrist, it seems to me --

1) As you constantly compare yourself to others, it may point out to a few things but I think as you mentioned other complications, it must be bad childhood. I know it may at first sound weird to you, but you said you weren't "good enough" despite the fact that you graduated with a psychology degree (I am a science student too! Not from the West though.)

2) You view yourself in a negative light a little bit too much. "I feel bad for.... [things that you couldn't do in time]" and this attributes to many things ranging from low self esteem to delusional guilt.

I think you should talk to your GP about this.
[Personal note : I don't think you can attribute you not doing well at school as a negative point. I mean, I myself suffer from a lot of issues too and all I can say is that they're not in your hands. Being gay or not isn't in your hands.]