How do you know when you're depressed?

I'm very stressed out lately. I finally went back to High School this September and it's been really stressing me out. I'm 18 and I have been with my SO for what will be 4 years in May but I just broke it off because I can't handle anything right now. I have anxiety that's getting worse since I stopped taking my pills a long while ago and it's getting involved in my relationship. I have been wanting a family for so long now but I'm not in the right place for it and I want my SO to be more committed to it but he don't want it right now either. Every time a problem comes up I break up with him I can't handle the stress and I'm constantly feeling depressed. When just a simple argument come up suicide keeps popping my mind, I'm wondering if life is even worth it anymore but again I don't want to die but I want to stop feeling this way. I'm scared to die but I can't put up with feeling this way much longer, my mind keeps making me think that my SO doesn't love me and that I will never have a good life. I feel like he doesn't care but he fights for me back even when I'm very cold, hurtful and bitter to him and I love him soooo much but I keep doing this simply because I'm depressed. I'm pushing his away everyday.. How do I know if I'm depressed and when I really need help? How do I talk about it to my family?😢