Her giving in to her desires has nothing to do with immaturity. She has a physiological condition, which makes her incredibly horny all the time. It's like being high on drugs constantly, which means she's always open to temptation, and it requires a huge effort on her part to resist. When people are in that state, it's very very difficult to consider consequences. But unlike people who use drugs, Anna hasn't chosen to be like that, it's the consequence of an accident totally beyond her control. So I think comparing her and Andrew on that basis, is meaningless.
As far as Andrew is concerned, I don't think he's responsible at all. He relies on her to go out and make money, and makes excuses about why he can't get a job. I mean when you're in their position you take any work you can get. And not just wait around hoping to get the perfect job. Even the job he does get, it was Anna who got it for him. If it was up to Andrew, no doubt he'd still be unemployed.
Anna is doing multiple jobs to make a life for them, and then she has to come home and do all the housework, while Andrew sits around watching TV. Never once does he offer to help her. Even Ashley helps her in the kitchen, and he doesn't even live there. If Andrew was responsible as you claim, he'd be trying to support her as much as possible.
And then when they move into their new apartment and Anna is desperate for a romantic night together. Andrew decides it's perfectly fine to go off and hang out with Ashley for a couple of hours in the middle of the dinner. Once again selfishly putting his own desires above their relationship. After that Anna gets drunk, and that's what leads to her finally giving in to her lust and having sex with Alfred ( the first time she truly cheats on Andrew). Andrew's irresponsibility could thus be said to be the main spur for Anna becoming a slut. Perhaps if Andrew had stayed home, maybe she never would have had sex with Alfred, and never would have had sex with Ashley, Carl and Sergey later that week? And maybe then, she never would have realised that Andrew wasn't the best in the bedroom?