It's clear that you are an empathetic, kind person, just based on how you talk about your loved ones. Don't take that for granted, but love yourself for it, these are wonderful qualities that too few people have.
Depression comes in cycles for me, too. I'm surprised I've still made it because I'm on my 5th cycle now (I'm 23). I try to take each cycle as an opportunity to learn more about myself, and the patterns I experience. Now that I'm on my 5th cycle, I've learned that I get depressed in times of transition, usually after I finish something I enjoyed in the moment, but now find meaningless. And I understand that when I'm depressed I want to self-destruct, make myself seem as hopeless as possible to get some sick "revenge" on other people, I view people who want to help me as selfish, etc., but I always snap out of it eventually. Since I know that, I'm able to hold back on my worst desires. Even though the other day I still freaked out on people, I was able to warn them in advance, for example. Or I know not to do anything that would give me permanent damage because I've recognized that my particular depression doesn't last.
I don't know your situation (feel free to message if you want to talk!) Though yeah, if you know deep down that there are times in your life that you were happy, and that you can return to those times at another point in the cycle, use this opportunity to learn as much as you can about yourself. Write down what you're feeling, try different strategies, eventually you'll be in a better part of the cycle and you'll have more tools to manage your next episode.
