One thing you might want to do is to ask yourself whether what you're thinking about or feeling is useful.

We can't always control what thoughts and feelings pop up, so you're going to have periods where you think back to things you did and feel guilty and ashamed. But ultimately, sitting there and wallowing doesn't actually help anybody or anything. Nobody's life is improved by you feeling shitty for extended periods of time.

So when thoughts like that come up, acknowledge them. Yes, you did some awful things and that sucked. Addiction is an awful thing. But you are living in the now, not the past. What are you going to do next? What kind of people do you admire and what do you think they would do right now if they were in your place? What kind of world do you think you'd like to live in? What do you think is good and important and worth fighting for? What do you think sucks and is worth fighting against? And is obsessing about the past the most useful thing you could be doing right now? If not, what could you do instead?

It doesn't really matter if you used to be horrible or not, because you have choices NOW. You can choose to not be horrible now, and to not be horrible in the future.