I have to wade in on the single mum thing. There isn't an automatic connection betwen being a single parent and poverty you know. Just as there isn't an automatic connection between being in a relationship and having a lovely house / school.
I was a single parent for a few years until I remarried. Worked full time. Nice home. Well educated DCs. It's important that you think about this as a) your views on this are so far off the reality and offensive, and b) they could be keeping you in a relationship that isn't a good one.
The time to get married (assuming you want to get married) is before you have children. Why would you want to have children with someone who doesn't want to commit to you?
But of course you can't travel back in time, and have sympathy for the situation you now find yourself in. Your bf could be stalling because he just doesn't want to marry you / at the moment he knows that if you split for any reason he will be financially better off than if you married (and of course you would be worse off).
Or it could be that he wants to get married 'one day' but is too lazy / doesn't care enough to do anything about it.
So - I suggest you tell him 'We've talked about getting married for xx years. It's ridiculous that you are stalling. I suggest we make sure we're married by xx date this year. If you say no, I'll assume you never want to get married. If that's the case I'll be re-evaluating our relationship as it means you've been lying to me, and stringing me along, for years, and are happy to see me suffer financially if we split. I'll also be taken all the legal steps I possibly can to ensure that I get all the same protections.'
If he continues to stall, go and get some legal advice. Explain the issue and see what you can do to protect yourself as much as possible.