Should I tell people about my Anxiety and Depression?

I have suffered with Depression and Anxiety for a few years now, but I've noticed over the last few months, it seems to gradually get worse. I always feel alone and frustrated with myself and I have lost interest in everything lately. I've already told a few really close friends and it seems like they don't really care. I'm kinda afraid I'm going to do something stupid that's why I feel like I need to tell more people. I feel that when I talk to my friends about it, it somehow feels a little bit better. I really want to tell this girl that I suffer with depression and anxiety because she would always talk to me in school, I want to tell her but what if she thinks I'm a loser or something. I just feel so frustrated with myself all the time, I keep getting all sorts of negative thoughts and I feel I need to let people know in case I do something that I regret. I'm also very shy and not outgoing at all, and it's very difficult for me to open up to people because I have bad Anxiety as well. I only have a few close friends. I'm 18 by the way and I have felt like this for the past 3 years. I would usually try and put on a happy face and it would work but recently I find it hard to pull that off anymore, even my parents are starting to question my mood swings, but I just tell them it's nothing because I don't want them to think that I am a loser or a weirdo. Do you also think that I should let this girl know about my depression, she is a outgoing person but I have a feeling that If I tell her, she might swear at me or call me attention seeking or something, but I'm not. It's just that I've kept it in for 3 years and only 4-5 people know about it. It's getting worse and worse and I feel like I need the support right now. I feel if I don't tell people then I might end up doing something stupid. Thanks please don't be harsh with your answers.... Yeah I know I'm pathetic