Can you change the past? No.

Can you change the future? Yes.

I think you're placing a lot of importance on things that don't matter. There's only one real thing you can achieve in life, which is to enjoy it. Anything else is secondary.

Comparing yourself to the best parts of others will always fail as you're more aware of your own failings than theirs. Life isn't a competition.

As for being convinced things cannot get better, try changing the things you can and see if elements of your life improve.

I do think that you might get better results talking about it with close friends or a professional rather than random people on the Internet, but focusing on your regret stops you from moving on, which is why it's important that you don't.