I have so many friends but I feel so lonely and depressed?

Patient: I’m 17 years old and I have so many friends, I spend time with them on a regular basis, they are there for me, and they do everything to help me when ever I need help. I spend lots of time with them, I love them all and I tell them anything and everything because I feel so comfortable around them.Yet, I feel so lonely and depressed. I’ve told them this, and many of them assure me that they’re there for me and I can go to them if I ever need anything, but no one seems to know the cause. Everyone would be having fun and laughing, and I would be there completely dead inside and all I do is put on a smile and a normal face and pretend like nothing is going on.I have liked this girl for about a year now, but I’m not the brave type that would approach her and tell her. We’ve been friends for a year now, and we get along so well and we spend so much time together. A friend of her’s told me that me and her are really close, and she knows for a fact that she does like me, but I was too stupid and I did nothing about it. Now, more recently, I finally managed to get the courage to tell her how I really feel, but all she said was “I’m sorry, I only see you as a friend”. Her friend says that she probably got over me since she thought that I didn’t like her. So we’re still friends now and when ever I talk to her, I act like I’ve always acted, but like when I’m around anyone, I just feel so depressed, lonely and gloomy. And yea, this whole thing pretty much started when I got turned down by her.This was my first time I’ve ever told a girl how I feel. She was actually the first girl I’ve liked enough to actually tell her how I feel. I have told a number of friends about what happened between me and her, and they have pretty much all given me the same advice, but nothing seems to help me and my lonelinessI don’t know what’s wrong with me. Even at home, when I’m trying to study and stuff, I always seem so down. When ever I’m doing something fun with friends, I’m enjoying myself and if for some reason I remember what happeend between me and her, I instantly become crushed and I just feel like crap. Some advice would be really helpfulThank you