The couple split last year when Cottrell was charged with assaulting the actress during a heated row. Cassidy, who confirmed that she was back together with him last weekend, explained how alcohol had been an issue in their relationship from the beginning.
"We met at the Isle of Wight festival, it was a whirlwind romance," she told ITV's This Morning. "Adam moved in quite quickly and I was living in the West End at the time and we went out, partying and drinking and having a great time with friends.
"Then I was doing Strictly Come Dancing and then I fell pregnant quite quickly... and suddenly I didn't like Adam when he'd had a drink, because I was sober.
"Adam and drink didn't mix really, from the beginning, and I'm not great when I have a drink to be honest, I don't think anyone is, but it did change and it got worse because I was permanently on edge.
"So when Adam was to have one drink, everyone else would be, 'What's the matter with you, he's fine', and I'd be like, 'I don't like it, I don't like it'. So I'd put pressure on him and then he'd have another drink."
The ex-EastEnders star told hosts Phillip Schofield and Emma Willis that it was "quite hard" for Cottrell to know she was discussing the situation. However, explaining her reasons for doing so, she said: "I think sometimes you sign up to things.
"Adam and I did a documentary following the birth of my baby and all of that and people got to know us, and with magazine shoots, and sometimes it bites you on the bum and sometimes you have to explain to people what's happened because they deserve an explanation, and also as you know, if you don't tell the truth, then people write rubbish.
"So I'm here really to talk about it for the last time, to put a line under it, explain to you what's happened, how happy I am and then hopefully move on to some really good work."
Cassidy continued: "I think it's quite hard for him, it's hard for everybody who's close to me - I've done all this in my private way with my dad and brother, so it's hard, but it's got to be said really.
"I can only go by my story, and people on Twitter have been saying... I'm getting great support, some lovely people supporting me and others saying, 'You're mad, he'll do it again'."
Recalling how a reunion had come about after she dropped the restraining order against Cottrell, Cassidy said that he had suffered a "frightening relapse", prompting her to realise that he was not a "horrible person".
"He got some help and I was there as a friend and we just became stronger and stronger and I thought, you know what, we can beat this together," she said.
"The things that happened to me, the violence and mental stuff that happened last year, although terrible and I'd never condone it and it was awful, but the biggest thing for me was the alcohol and the complete panic and being on edge and wondering when Adam was going to get moody after one drink.
"And without that in our lives, I cannot express how life is amazing. He's a totally different person, the programme he is on now addresses every issue. He says he's an alcoholic now."
On the future, Cassidy said that the couple are taking things slowly, but insisted that the relationship would end if "anything violent was to happen again".
"If Adam was to go out and have a drink again, I would have to address it... but I haven't got a crystal ball, I don't know what's going to happen, but I know 100% that if it carries on and if Adam continues to do what he's doing, I really do believe that we're gonna be really happy," she said.
"Many people that I've spoken to have had a positive outcome so I'm hoping I'll be one of them."
> 'EastEnders' Patsy Palmer backs Natalie Cassidy abusive ex reunion