I Am Depresed

I have not been officially diagnosed,but I do feel this way. I feel incredibility alone,even though I am surrounded by people who love me. I have tried talking about it and everyone says "no you're not,you can over come this feeling,you just have to change the way you think." My best friend told me that,after I poured everything out to her. How does this make me feel? It makes me feel like I should just stop talking. No one is listening to me,maybe despite having people around I am indeed alone. I feel like everything is falling apart and like I'm looking in from outside as my life crumbles apart. I have tried to change the way I think, i have tried to keep it together,but I feel like the seams are forcefully being pulled apart.