How would you feel if you had never heard of AS and didn't know such a thing existed?
What would you blame your foul attitude on then?
Or would you just get on with life and make the best of whatever comes?
'Cause there have been millions of people who have lived with the same handicaps who never had a diagnosis to blame it on, they just had to press on and manage.
But you're right, you do obsess and think too much. If this is how you are when you HAVE a girlfriend, sheesh. What's the point in wishing things were better when you refuse to enjoy the good things you already have? Can you not see how illogical your logic is? You think you only have the girl you have because of your looks, but if you lose her, you're certain you'll never meet another girl who will like you. Duh. If your looks attracted one, they'll attract another. As for losing the girl you have, well, I won't blow smoke up your skirt about long-distance relationships, but I won't speak for her. If anything drives her away, it will be your bitter self-loathing. Nobody is going to want to be around a curmudgeon in constant despair that the end of the world is imminent and unavoidable. Lighten up, for your own sake.
You are ONLY 23. It's stupid to make pronouncements about the REST OF YOUR LIFE. Trust me on this, you HAVE NO IDEA what life has in store for you over the next 23 years, or after. But what will make those experiences positive or negative depends almost entirely on HOW YOU CHOOSE TO PERCEIVE THEM. If you think everything's going to suck, it most assuredly WILL. If you believe there's hope that there will be some good, some not-so-good, mixed with moments of joy, that will be reflected in the experiences you have. Most of what happens around you, with you and to you is neutral - how it feels and how it works out depends largely on the lenses through which you CHOOSE to view it all.
Read Richard Bach's short novella 'Illusions.' It's a very succinct illustration of how to adjust your thinking in order to change your personal reality.