@Bobbingalong39 first of all I’d like to say I’m sorry you are in this situation. It’s very hard when you are in the thick of it to see if things are wrong, what the other options are, how to make the changes - do the changes even need to be made etc. So I understand how you’ve ended up at this point.
I’d like to ask you to take a minute to consider something, if you don’t mind? You say you have a daughter - 21 I think you said? If she moved out into her own place I’m sure you’d feel extremely proud. How would you feel if she told you after a few months she was moving her new boyfriend in with her? A boyfriend she had only been seeing for 4 months. What if she then told you he was only paying £200 a month towards the bills and food? Would you be happy for her? Or would you, as any mother would rightly be, concerned for her? What if you then found out that he drank heavily, gambled (and borrowed money from her occasionally, although always paid it back) and spent £1k a month on something frivolous (a car, a video game, home and away tickets for him and several mates to see their favourite football team, etc)? What advice would you be giving her?
I like to hope that should you see your daughter in the situation you are in, that you would tell her to put herself first and kick him to the kerb!
Why don’t you deserve to put yourself first? Everyone has, rightfully, talked about prioritising your children - but think about yourself too. You deserve better. Look at yourself in the mirror and repeat it until you believe it. Because I think your self confidence is shot, mostly from your ex husband leaving you for another woman, but also by being taken advantage of for 6 years by a man who is supposed to love you. A few posters have suggested therapy, and I think it would be worthwhile looking into that - perhaps you could fund it with some of the extra money your BF is going to pay you! Maybe there is a way to salvage your relationship and not be taken for a mug, if that is what you truly want. Or maybe it will make you realise what you’ve put up with for so, so long now and you will understand you never deserved that. Your self confidence and self worth is so shattered right now, you think this is what you deserve. It’s not.
Another thing to consider, and I think a couple of the later posters also highlighted this, is work out how much money you would have been able to save had he been paying you a fair rate. Even £600 a month would have been over £40k into a savings pot for your retirement fund, or for helping your children into the property ladder like you hoped you could. And that would have still left him with £1,800 - £3,200 a month to do what the hell he liked with! He could have even still kept the expensive car and had money for going out and having a very, very good social life. Out of curiosity, how much money do you have left over a month to spend purely on treats or days/nights out for you and/or the kids?
Your kindness has been taken advantage of. I completely understand your logic of wanting to make sure he had no stake in your home, that you’d still be paying the bills if he wasn’t there - but by the same logic he’d have been paying bills if he were living somewhere else. When you move in together, the idea really is that you BOTH feel the advantage of saving on your monthly outgoings.
Sorry that was so long - I know you’ve struggled to read a lot of the comments on here as people have become frustrated at your reluctance to open your eyes wide to the situation you are in. I hope you will see we are all just concerned about you, for your children and your future, and are just trying to get you to see this man for who he really is.
Good luck - I hope you get the therapy to help you improve your confidence and self esteem, and I hope your belief in this man is correct and that he pays his way, gets help for the drinking and gambling (and the drugs if he’s still using) and becomes the man you deserve. Honestly though, I think you would be better off without him, and I think you’d find a huge weight lift off your shoulders if you were to kick him out.