You ARE that. They are judging you in the present moment, as everyone should be judged. It's not like you're still going out and doing what you used to do in secret. You really do deserve to be judged on who you are right now.
And you have a right to say "I AM a good person" if that is what you are right now. There is no deception in saying that. You're not saying "I have always been a good person". Who ever says that anyway?
Maybe your new love interest has a "dark past". Who knows? Who cares, frankly. What matters is the love that the two of you share in this moment - the only moment that ever truly exists.
What happened to this past you speak of? Where is it now? Don't say "in the past"

In your mind, in the form of a memory. So it only exists in a metaphysical sense at most.
Thoughts only have power over you when you identify with them - when you believe you are them. The key is to de-personalise your thoughts and just observe them as "events that are happening in the mind"
When these dark thoughts/memories arise, instead of thinking "I can't believe I did that, this makes me a horrible person, what if people find out my dark secret?"
...simply think "Do I, in this moment, want to do those things?"
Obviously the answer will be "no", if you have truly changed.
So you're treating thoughts that come from memories of past self actions in exactly the same way you would thoughts of actions in general you morally question.
Do not make it so personal and get so emotional about it. Let your rational mind make the judgements, but don't get caught up in how bad that makes a person (whether you or someone else) or what it tells you about the person, because in reality the person is just an infinitely malleable construct of memories, values, beliefs and genetic information.
What are you underneath all that conditioning? It has no memory, no personality, no emotion, no sense of good or bad, yet it is the one thing that you can truly say, without any external evidence, exists in this moment. It is the silent watcher of all those aforementioned things.
Every time you make a judgement about "who you are based on your past", who is watching/hearing that judgement, and are they the one being judged?