You can't go on like this, Oddish. If things are generally good between you then you'll have to stop prodding the hornet's nest because that's what you're doing.
In my opinion there's no way for you to 'win' because if things are going well, the other person thinks, "Why upset the applecart?". There's basis for that too as many couples who were fine unmarried, suddenly break up after marriage. Of course there are many other couples who don't but that's immaterial. A dissenter has rightful evidence that this could happen.
And, if things are getting tetchy because you're not getting this one thing that you want, the other partner could be thinking, "Well, we're a bit shaky, keep arguing about this and she's not letting it go so there's no way I want to make this a formal thing".
You can't win.
You want the romance, that he wants to marry you more than anything and I just don't think you're going to get that. The time, as other posters have alluded to, was before you had a child together as most men understand that women generally won't have one before they marry if this matters to them. It didn't so it doesn't, as far as he is concerned.
The only sensible thing to do is put marriage out of your head as an option. You don't want to leave him so the only chance you'll have to make him consider this is to be happy with what you have. Sounds counterproductive but it isn't really - if you're generally happy with your lot then celebrate it.
I don't think you'd be happy with a marriage that you feel you've wrenched out of him because you'd always know that you did... so re-frame now. You don't need to be married and you don't want to marry somebody who doesn't want to marry you. His loss. :)