I think a lot of us have been where you are right now. I know I certainly have. Frankly, it took a lot of character, courage and openness for you to post this out here. Those are three pretty awesome things, so if you think about it - you have a great foundation. You also have a gift from the sound of it, for some very academically challenging areas, so you're intelligent too.
Insecurity is an awful thing. I've done battle with it before and sometimes still do from time to time. But something I have learned along the way is that insecurity is one of "the great liars". The only "strength" insecurity has is the strength you give it. And you can starve it and defeat it in an instant. Nobody has the right or power to make you feel insecure - you have to give them permission and then enable it.
Take a good look at yourself, and with a different perspective. Look at all the things you have accomplished, that you have to offer and that you are - and for crying out loud, do NOT sell yourself short because of something that someone else MIGHT think. Yes - this is all about you. And you're worth it, don't you think?
Let me relate a bit of my own story here:
Just over three years ago, my (then) partner of 3 years dumped me to have an affair with some guy that he met on Craigslist. Shortly thereafter I found out through his admission that he had cheated on me the entire time we had been together. I realized I just was at the end of myself. I knew he had been cheating and it drove me to drink, my diet was atrocious and I let myself go. Self-esteem? Gone. I felt exactly as you do now - like I just wanted to be happy, like I was alone and unwanted. And one day as I was sitting there amid the physical wreckage of myself, I decided I'd had enough.
I realized I had "nothing and nobody". But the inescapable truth was this: Though the tornado of my ex had leveled the ranch, the foundations were still there - unscathed. And then a realization hit me and this is true for you or anyone else sitting where you are - I realized that my life belongs to me and that I can build my life, my body and the man inside into anyone and anything I want them to be. My ex, in doing what he did - did me a favor because he showed me, unintentionally, that you can get rid of all the garbage in your life and build exactly what you want.
As I did this I found myself working through issues that had plagued me since the 3rd grade. Being a gay kid was tough to say the least, and being massively disliked because of being the "new kid" in my school, plus the crap I took at home - well - you get the idea. For years... no decades... I had tried to beat, pound, mold and package myself into an amalgamation of this person I thought others wanted me to be and I was MISERABLE.
Here's some genuine hope for you - and this is not "hope so hope" it is KNOW SO hope because as I type this - I am living it. Once you find your foundation and get rid of the garbage that is stopping you from becoming the man you truly are and are meant to become - you are going to grow, develop and absolutely shine like you can't imagine. Happiness? That's an emotion - Opt for joy which is eternal and unstoppable by anyone except you.
And it's OK to feel the way you do right now. That's human. But don't let it become a way of life. You are not alone because there are a lot of us out here in the gay community just like you. There are a lot of us that are here for others if needed. It's just what we do. "Alone" is a sad illusion and another lie we tell ourselves. Unwanted? I doubt that very much. You have friends, you have classmates and people you see every day. You matter very much to a lot more people than you give yourself credit for.
You're not desperate either - you're human. You are at a wonderful new starting point and beginning. You are standing on the edge of something truly amazing and when you let it happen - you'll trade an existence for a life.