Hey, mental health and relationships can be really difficult, especially when you're young. I went through my toughest mental health issues when I was around your age (assuming the range you have set is correct) and it can be hard to get yourself out of bad spots. My suggestion would definitely be to try and find people you can really connect to, maybe join a club or sport you're interested in try and find someone you enjoy talking with. When it comes to venting, it can be a good idea to get permission first. Once you find someone worth your time (and honestly, based on the small amount of info you've given, your ex bf and bff do not sound worth your time) try saying things like "Hey, I'm having a rough time, do you think we can talk about it?". That's a really good way to make sure the person you're talking with is okay with the conversation, sometimes people are going through their own things and don't have the energy to talk or help with others. A good friend, however, will find or make the time and energy for you at some point, it may not be immediately, or they may offer to help in other ways.
But my biggest piece of advice is to not be so hard on yourself. You are doing your best right now, and that's all you can do. Surround yourself with people who make you happy, and try to stay away from those who make you feel poorly about yourself. You got this.