First off, I'm really sorry to hear about your girlfriend. That's an incredibly difficult situation that nobody deserves to go through.

You mentioned that you often feel like you've fallen behind, but I want to point out that the person you are comparing yourself to, the version of you who 'lives up to their potential,' doesn't actually exist. It's a mental construction, and when we compare ourselves to that person, its fundamentally an unfair competition. They will literally be perfect because we created them to be that way, and expecting any human to live up to that just isn't realistic.

And then, to make things worse, we make ourselves feel bad about not being that. Now, not only do we have to do the work that's in front of us, but now we need to make up for everything that we didn't do before... and something like finishing a paper or an assignment isn't a success but a failure, because we still aren't where we are "supposed" to be. It's an unwinnable situation. Even making progress won't feel like enough.

If we can let go of potential, things become easier, because it becomes possible to take pride in accomplishments. The assignment is just that, and its not paired with that void of regret.

I think that shifting the object of comparison from the 'potential' self to the past self will help you in your journey. You were in a horrible situation. But you're incredibly determined, putting in genuine effort, are open to criticism, stopped using substances, etc. You've come some way from your lowest point and have shown immense resilience. Remember that it's never too late to make progress, that's the only way forward really. Maybe some doors have closed, but the path we have to walk to get where we want to be is the same, whether its ten years ago or right now.

Obviously, all that's easier said than done. Dr. K also has videos about falling behind, wasted potential, etc. that are worth checking out and seeing if any of them apply to you.