Elendon I have not read all the responses from others but have read some and I have tried to read all your posts. I noticed quite early on that you said you were/or might be depressed. I think you really need to get some help for this, maybe the Samaritans would be a good place to start and/or the GP.
It sounds like you have had a really shit time with your ex and he is royally screwed you and abdicated responsibility for your oldest child. This is bound to cause some considerable degree of stress.
It is clear from what you say that your desire to move your daughter out is because you think this will be best for her. I think in reality this may not be best for her at all but I think you need some wise voices from people who can advise you how to approach the issues.
I am not in any way a professional but it looks like from some of the posts here some wise people have waded in with some really good advice. As well as a few very rude comments!
I think it is time to be honest with your dd and her boyfriend about your desire to move and your desire to be able to get your head above water finance-wise - in a suitable way, take advice on how to do this from a mental health specialist, please. Although her boy friend is not your problem it sounds like you do feel he is good for her so could you have an honest face to face discussion as adults and explain about the needs financially.
If both your dd and her boyfriend could get jobs, even quite basic jobs, that would enable to them to raise the household income to a suitable level. Not just scraping by! Actually being able to pay all the bills and put some aside so that if/when your dd moves on then you will not be left in the poop!
The other adults in the house need to see themselves as adults contributing to the finances and helping with the younger kids, if appropriate, not in a scary way, but in a sense it would be more scary (I think) to just be told you need to move out!). You, I think, need to move towards that before your dd will be able to move out and be independent.
Please do seek some professional help for you and your dd, get a proper medical diagnosis for your dd, go with her if you need to, please.