Well you could continue as you are!
It sounds as if you are happy where you live. You have your parents to help you out.
Your children are happy where you live.
You've got a job.
It doesn't make any sense for you to move!
You see your boyfriend two or three times a week. Of course you can have a relationship. You're having one.
But why do you have to throw all your security up in the air to have it? That doesn't make sense.
Until somebody actually lives out of the family home, there is a limit to how much proof of adulting they can provide. Are there any exceptional circumstances here eg he does a lot of caring or some such? You me tion he is naive....sounds worrying.
And if he's going to buy a property he could buy one nearer to you if he's serious about you living together in the future.
I understand future planning, but to plan having a baby with a man who hasn't even moved out of the parental home - that doesn't make any sense, wait till he makes progress in life.
He can buy a property. You stay put, see how things go. If that works, it still doesn't make sense for you to move nearer his parents, unless there's a half way compromise. If the argument is his £50k job, that can go pfft any minute.
What are his actual plans to buy and if he can do it, what's he waiting for? And this will seem harsh, but do you know for sure he earns that much?