> I don't really exercise much, but at least I go on 30+ minute walks every other day or so

I strongly recommend something more intensely cardiovascular for 20ish minutes a day (I go on runs). There's a lot of clinical evidence for aerobic exercise improving concentration and mood in a way just walking does not.

> How were you able to function in such suffering for 10 years?

I didn't function terribly well for that time period. I kept going mostly out of a desire to not hurt those I love. I was fortunate to have a supportive family and to be smart enough to coast through life while functioning at a massively reduced level.

> What led you to getting better?

I think some of it was just the maturation process that occurs between 20 and 30, but a few things stand out:

1. Really increasing the self-awareness of what I need to maintain my mood (the humans are complex houseplants bit). For example, if I'm not productive for a week I feel bad. If I'm tired I'm not productive, and thus I'm very pro-active about taking caffeine if I feel tired in the morning. This requires a lot of mindfulness and self evaluation, zen meditation can help here though I don't think it's required.

2. This point merges with (1) slightly but is worth breaking out, realizing the motion usually precedes emotion. When I'm feeling really bad it's often because I've failed to maintain the habits necessary for me to feel good for a while and usually it's going to take at least a week or two to work back to feeling good. As an addendum, any psychological tricks you can play on yourself that prompt the kind of action you know you need intellectually but can't bring yourself to do emotionally are gold. (I often tell myself I'm going to workout for 10 minutes to get myself up to 40-50 minute workouts).

3. I learned that while taking time to think about what makes you sad and unhappy is initially useful as you process your emotions, there comes a point where you are just wallowing in the misery. A depressed mind often gets caught in "loops" that are hard to break out of where you run through a negative line of thought over and over again. If you spend 60 minutes thinking about something wrong in your life that you've often thought of before and found no new insights, you've probably just made it a little harder to break out of your depression. Learning to short circuit these trains of thought really improved my mood.

4. As a personal thing, the realization that I was never going to be as happy as an adult as I was as a child and that that was actually ok (I was raised to believe being happy was all that mattered in life). I learned that feeling fulfilled was a good substitute for feeling happy and now feel life is worth living. It doesn't sound like this is a problem you have though.

> How do you look back on your 10 years and say "it's OK, I needed to go through that/I'm happy I'm better now"?

I don't. In retrospect with the right conversations I probably could have gotten out of the funk in 2-3 years. But going back to point 3 of the list I've learned there's not much point wallowing in it (I still do occasionally, I'm not perfect). So when I find my mind wandering to that thought I move it to something else.