Was just going to say this. He's got everything he wants now: you're living with him and you've had his baby. All the power lies with him and he knows it. You should have insisted on marriage earlier than this. The early years of babies are also testing for any relationship so he may now be thinking of holding off so he's free to bail down the line without the commitment of marriage. Sorry OP  This is why women really need to insist on marriage before letting a man have all the benefits of marriage without proper commitment on their part. If a guy truly wants you and is committed, he will want marriage on the same timeliness as you. If he doesn't, women need to dump and move on. Stop moving in with boyfriends without commitment.
Sorry, but I think this is a really unnecessarily cynical and pessimistic reading of things. Loads of people want their wedding to be the magical, emotional day they imagined, many of us on this thread have said we feel the same as OPs partner.
There is a very real argument that he's being naive about the practical side of it, and OPs need for security when giving up work etc. But it's highly unlikely that he's deliberately hoarding power, hedging his bets for an easy exit, and also just not true that if he was truly committed he would want to be married ASAP above all other considerations. If he's truly committed, he may see it as not making any difference when they make it official, however naive that may or may not be.
It's far more likely that, just as he says, he actually does just want to have his wedding with his loved one's present, for the sake of waiting a little bit.