I honestly think you're doing this for all the wrong reasons Red. I think the main driving force is your health and the worry that you won't cope alone with DD. Would you at least look into your options where that's concerned? Check whether you can get out of your rental contract on the grounds that your health has deteriorated, look into what other help you could get, either from family/friends or social care so you could manage in the new place. I think at least half of this is about needing help rather than needing him.
The other half is harder to deal with, you can't (or won't, for the reasons already mentioned and because you still want to see the best in him) see it but he's sucked you back in.
It's already been pointed out that he's promised more than he's actually done, it's all 'when this happens I'll....' rather than actual, physical progress. He's talked you into being ok with him giving you no money because 'he has to live', yes and so does his daughter and if she didn't have you and your mum and the safety net of there always being someone else who will feed and clothe her his DD would be going without. He's refusing to do the one thing you've said is essential, therapy. Despite the fact that, once again, you are spoonfeeding the solution to him by paying for it. And he's talked you into seeing things from his point of view, the 'just 2 spliffs', the 'I'll give you half the deposit money when.....', you're making too many concessions already and that's before he's even moved in!
And you still can't talk to him about 'tricky' subjects, money, therapy, the old flat. How much of that is your own fear of confrontation and how much is that he still makes it too hard, too uncomfortable for you to raise with him? This is all stuff you need to work on for much longer in therapy, your boundaries and ability to defend them, your ability to communicate about things you find (or he has made) difficult without fear of it being 'awkward' or him kicking off. And he needs to do a lot more too, kick the weed completely, start therapy, hold down a job and prove he can support his family.
Other than the need for help because of your illness, the fact that you feel like you can't back out now you've 'invited' him back and the picture you've painted in your mind of the 'happy family' you want to be (which is extremely likely to differ significantly from reality) why exactly do you need to get back with him now? I can see a multitude of advantages to waiting, taking things slowly and not rushing in and absolutely none for going ahead with him moving straight back in. At least find out if there's another way round the practicalities (alternative help/whether you can get out of your rental contract) before you make a decision because your other reasons are just not strong enough for the risk you would be taking by getting back with him at this point.