If he's usually only interested in short visits, ad hoc, and nis now asking for proper time I suspect one of two things has happened:
1 He wants to reduce whatever child payments he is making (or you have now asked for proper child payments and he doesn't want to pay).
2 Someone, most likely his partner and/or parents, have made him feel that he needs to be stepping up more (whether or not he will is irrelevant).
His partner being in or out of the house is completely irrelevnt to the court. So drop that as an issue.
If he has not had the children overnight at all, you could arguably suggest a period where you build up to this level of contact - eg perhaps one night every second week to start, then one night plus the mid week, then EOW plus one night in the week.
As I understand it, if you go through this route formally, even if you don't actually GO to court, the court would stamp it and sign it off? In which case, theoretically, he would have to abide by th enew guidelines (and you could include under what conditions ad hoc visits/trips/contact would be okay). But enforcing that would be difficult.
If you believe his drinking genuinely is an issue (and I'm afriad it's hard to really believe you do because otherwise why are you so relaxed about him taking the kids out all the time), you could use this as a reason why he should not be granted overnights. But I think you would need real proof of potential harm not just a general, "he drinks to much".
I am inclined to say that once you agree the new contact arrangements, the best you can do is act as if he will do whatever it is he has agreed to. If he doesn't, make sure you go back to court to ensure you then go back to the increased CMS payments.