Please stop making threats to leave, and for God's sake stop asking your DD if she'd like to leave. That's just playing mind games with her - we left because DD wanted to [therefore she'd see it as her fault if a move doesn't work out].
Go out with your partner and have a drink and make some plans. Are you together because you can't be arsed to split up, or do you actually deep down like each other but are just in crap circumstances? Could you move as a family to a new area, away from your parents and his job and his dealer and give you all a fresh start. If you struggled to get into university, could he get in, would he appreciate the chance to train for a new job, or maybe go self employed?
Why didn't you get into university? Was it just the sheer volume of applicants trying to get in before from the £9k fees, you applying to a too academic university or a lack of relevant work experience, for example?
I remember moving into our house and being really unhappy, and then reminding myself that my DH wasn't any happier than me. We had to work together to improve. So, do you two want to split up or change your circumstances? If you just want to change circumstances, he has to stop smoking your savings away every night, you have to stop underminding your partner to your DD, and you both need to start making plans for a different job, different flat, different area etc.