You all need time to think and deal with reality.
First of all, you need to be brought up to speed damned quickly... His Mum new all along? perhaps she's been funding this??? God I hope so! Last thing anyone needs is to be saddled with immense amounts of debt..
Can I suggest you get him round to his Mums, sharpish. Sit them both down, tell them that as of this precise moment, all bets, plans and whatever are firmly on ICE, until you have the gospel truth.
Then, fold your arms across your chest, and say, OK, Out with it ALL!
That way he won't be tempted to continue with lies his mother knows aren't true...
I'd be seriously wary of marrying him at all tbh, if he can lie to you like this for so long, going through the rigmarole of getting up and going out to work for nigh on 2yrs, imagine what he can do when he REALLY puts his mind to deceiving you.
Don't agree to marry him under any circumstances until you are 100% over this, and have come to terms with it all, i.e able to laugh about it.
I rather think that once the full truth, the complete extent of the charade has been unveiled to you, including the etensive complicity from his mum, and your future MIL... then I have a feeling that you won't want to go through with it all. But if it does come to an end, know that you have done nothing to cause this, nothing at all.
Jeez what a horrible situation to be in, I really feel for you, it must be awful. If you can start to look for small mercies, perhaps finding out before the wedding is the first place to start.
Huge sisterly hug for you!