I [M18] am having troubles with my girlfriend [F17] and I don't know what to do

 We have been in this relationship for 1 year now and we have had some troubles along the way, that's normal for any relationship. Right now I'm having a tone of issues relating to where I stand with her and how I deal with the way she acts with other people and how she acts with me. 

To start off, she is very friendly with generally everyone, but inside our small groups of friends (mostly guys in the first place) she particularly calls him a "close friend". The type of relationship me and my girlfriend stand in is a best friend/girlfriend situation. But, at times she tells him, and even our whole groups things that have happened to her or how she feels that she hasn't confronted me about. These things aren't that big and/or serious compared to other encounters she has had, but I just feel a sense of weakening in our relationship whenever this happens. I get severely jealous at times, but I have been working on it and I do realize that she loves me and I love her, I am not worried about her cheating on me at all. The thing I am worried about is loosing the connection I have with her. At times I seems like she has more fun with this "close friend" than she has more than me. At times I feel like the only thing I mean to her is a physical counterpart, nothing more, all she wants is cuddles and anything physical. I mean, yeah of course I want that too, but I want an emotional relationship as well. I have confronted her about said friend in the past, but all it turns into is a fight, in one way or another. She gets mad at me for "not realizing how much she loves me." But when something like that happens, I hate for her to be upset, and I just try and take care of her. In the end, I feel like nothing really got resolved. 

 This happens for not just that topic, but for many. I might bring up how when I would be upset at something she did to me, she will then proceed to get upset because I'm upset, and then I'll have to ask her what's wrong, and in the end, I always seem to be the one at fault. (I apologize for the not-so-vivid picture I'm trying to display her) Is it just me being immature and getting upset at stupid things? Am I being selfish? I feel like I can't bring anything up with her about me because she will either have some way to twist it around so that I somehow was wrong for being upset, like if I brought this up with her, she would say something like "if that's what your really think of me then why don't you just leave" or maybe "I can't believe you would think I would do something like that to you" or some remark that would completely turn the tables of the conversation. But then when she is in the wrong, she bring up something like "sorry I've just been really sensitive lately" or "I can't believe you don't realize how much I love you" (the sensitivity part related to the next paragraph)

  At this current moment, and for a couple weeks now, she feels like she has no motivation to do anything, and whenever I ask about it, she tells me she doesn't know what's wrong. We looked into it and she thinks she has depression. I was a bit startled by this, but I didn't want to brush it off. I care about her a lot, and I don't want to see anything terrible like this happen to her, so I take care of her as much as I can. But in these past few days, she can't even take care of herself. I am desperately trying to take care of her, I will do anything and everything I can to make her feel better, its just sometimes I may get upset at something, and I feel like I can't come back at her and confront her about it because then she well back her self up with her being super upset the past few weeks and then I'll be the asshole.

Help, please

(Sorry for the length)

TL;DR. I haven't a fucking clue to be honest with you, I either don't understand women at all, or there is seriously something wrong with me and how I'm acting