Help.. please

I'm super insecure and I'm at the lowest I've ever been in my life. I was diagnosed with clinical depression a few months ago. Ever since then it's hard to do everything. I feel like with my relationship with my mans I'm ruining it. I get insecure because hes popular with girls because of hes social and track. And I get really insecure because they are so much better then I am. They are so pretty and I'm nothing. He currently is the only person I talk to in my days. I dont have anymore friends since they all left me without a reason. I just.. dont want to lose him. I feel like I'm tearing us apart. I feel worthless and useless. I feel like all I do is cause us to have a greater gap between us. He texts a close female friend sometimes and I enjoy her but with my sadness lately I feel like he is having a better time with others then me. I'm probably right too. We had an assembly yesterday and I cried after it. I felt worthless. I dont know how to change anymore. Please give advice.