I begin to cry whenever i think of how miserable i am (i have strabismus, glasses, i never had a girlfriend) or whenever i'm in a nostalgic mood. why?

Need help: Is you have a pcp, go and make a evaluation, ask for help, found out how depress, anxious, mood instabilities and related positive symptoms for depression and others possibilities. You can visit a psychology and psychiatric , they can evaluate , and help you with that situation .For strabismus , now are many treatment including botox, with good results, like others tx.

Depression: What you are describing sounds like depression. You should see your primary doctor to have some basic medical workup done first to rule out any medical conditions that can cause depression, like hypothyroidism. If you are "cleared" medically, you should then have comprehensive evaluation done for symptoms of depression. If your pcp doesn't have much experience, you should see a psychiatrist.