This won’t be the thing that fixes your depression, but congratulations on the financial security you have achieved! Like @Micro said, regrets are part of life, but they teach us and set us on a different path.
The majority of Americans can’t even spare $400 for an emergency. You have $6k. Dave Ramsey et. al. say you should have 1 month’s net income saved up for an emergency. You have 1.5 months’ gross saved, and that’s huge!
Your uncle’s situations were way different. For one thing, the housing market was a lot friendlier back in his day. Then there’s school, the sky-high state of anxiety people our age live in, on and on…don’t compare yourself to your uncle. His life was entirely different than yours.
You’re not “3 years away from 30,” you’re 27. You’re in your late-mid 20s. 3 years away is still over 10% of your life you haven’t lived yet! You’ve done a lot! At 27 I felt the same way you do, but feeling and knowing are two different things, and as much as I felt like a screw-up, I knew I was doing well. Focus on that. I had a house and that level of income, but I don’t think I had any savings. Maybe you’re not “crushing it” by your standards, but you’re succeeding objectively, and a lot of your peers would say you’re crushing it. How many people your age (not your uncle) are honestly doing better than you? How many people do you know who have houses paid off? By now I’m sure you know people that have gotten married and spawned little demons. I’d guess their houses are not “bomb-ass,” and I’ll bet that as happy as they are with their families, they’re exhausted, and wish they could trade places with you for just a day. The grass is always greener.
You can play the What-If game all day long. You are right, you can only go forward, and you can go forward armed with the what-if questions to make sure you don’t miss out on shit again. I’ve made a lot of mistakes and had a lot of “learning experiences” in my life, but the only things I regret are the things I didn’t do, and armed with that knowledge, the first thing I ask of every decision I’m faced with is “will I regret it if I don’t do it?” If I could go back with the knowledge…I’d have applied to an Ivy League school, but then again I probably would have been a C student in high school because I’d have known it was all bullshit. I probably would have still dropped out anyhow, I think that was just what I was meant to do. I’d have been bolder and dated a lot more women, but I wouldn’t have appreciated the special relationships I did have, even if most of them did end badly. I’d have kept my condo, but that would have stunted my dreams of creating a nicer homestead with my wife. I’ll be honest, these things haunt my feelings, but rationally I know that the path I’m on is the right way to somewhere.
I don't know where I'm going, but I just keep moving on.
If I could go back now and save myself the loss,
Substanceless character brought back would be the cost.