To be disgusted by who I used to be…

OP, you had an abusive childhood. It is very likely that the stuff you did in your teens was a reaction to that and an attempt to process it and make sense in some way.
Whatever happened with your colleague’s husband was not your fault. He is the one to blame. His behaviour was vile and predatory.
Would you feel able to talk about it to a therapist/counsellor? It’s a lot to carry about with you, you are a good person who deserves to be happy.

It's not your fault OP.

When you are cut adrift by your parents, the very people who should be there supporting you , and educating you, and helping you to negotiate life, then how can you be expected to make good decisions? How can you be expected to know how to cope with situations?
It's not your fault.
I agree with the pp who suggested counselling.
Fwiw my whole life is regret and shame .
But I at least recognise now I was badly let down by people who should have loved me better.

I think you have to let yourself off the hook OP and be proud of the person that you are today. None of the things that you mention are worthy of your continuing punishment of yourself.
You were a child who needed care and love. I’m sure that as a parent you can see that and you will strive to be the opposite of your own mother.
It’s really hard to sit with your past trauma and reliving it and talking about it isn’t for everyone.

I’m sorry for what you went through 😔Therapy isn’t always the best thing to help recovery; depending on your experiences you might do better learning how to master emotional regulation. Have a look at the Crappy Childhood Fairy on YouTube; she has practical techniques that can really helpXxx

I didn't have the same upbringing as you but also drank to excess and ended up in some awful situations (some of which I don't remember much of) so I empathise.

Honestly quite a lot of the issues I had were really down to the behaviour of predatory men. You were NOT to blame for your sleazy, rapey colleague's husband who no doubt took advantage of you.

Having said that, drinking too much and sleeping with men are not crimes. Forgive yourself, everyone does things they wish they hadn't. It's not who I am now and it's not who you are. It doesn't define us.

You poor thing. Withheld period products I guess? How awful for you. As an adult, what would you say to yourself as a child, if you could meet 15 year old you? Would you tell her how worthless she was? Or would you hug her and tell her that she is the opposite of worthless?

It's a very common theme for girls who's upbringing has caused low self esteem. You're far from alone in that past, and it's nothing to be ashamed of, its just a reflection of a troubled upbringing.

Therapy would certainly help you understand that you made the choices you did then based on trying to survive when you lived at home, and trying to find happiness when you left home. You have nothing to be ashamed of and your mind – your subconscious – needs to know that.

A good start is to understand your core beliefs; the way you learnt to view yourself and others in your formative years. This is a good guide;

https://www.betterup.com/blog/core-beliefs

I don’t think you did anything particularly wrong and I do think you need to stop fixating on it. We’ve all done things we regret as younger people, irrespective of our upbringings. I once said something so awful to someone I cringe every time I remember it; I didn’t mean it in the way it came out but it still has the power to make me want to wither up and die. All I can do is make sure I think before I speak in future.

Others may disagree but I don’t think counselling is good because it will encourage you to fixate on it more, not less!

Have you had therapy OP? you certainly weren’t responsible for the incident with your colleagues husband either