This was my reaction. You're reading between the lines a lot OP.
'When baby was born he stopped talking about marriage.'
'The realisation that he doesn’t want to marry me has crept in'
'An old friend asked my partner why he hadn’t proposed yet. My partner stayed silent '
'I feel like I’ve wasted my time if he’s realised he doesn’t actually love me or want to marry me.'
That's a lot of supposition to make you wonder whether you even love him any more! If I were him, I'd be horrified to get an ultimatum like that out of the blue.
Is it literally just about him not proposing... or is it that you don't feel as close as you used to? Most couples aren't as affectionate, romantic, or even interested in each other after having children as they used to be. When you're completely focused on a small child, and keeping the whole show of job, bills, mortgage etc on the road, taking each other for granted comes with the territory unfortunately.
But these things can be regained. The best place to start when you want to feel closer is to talk gently but honestly with each other about how you feel. I really like @Cardinalita90's idea of writing a letter, if you feel you wouldn't be able to find the right words face-to-face. A lot of us can't, ND or not.
My point is, you don't need to take the nuclear option of an ultimatum. Or equally, resign yourself to a life of quiet despair at feeling unvalued in your relationship.
Find out what's on his mind. It may or may not be what you think. If it is, and it's a deal-breaker for you and your child, then at least you aren't making life-changing decisions based on a misunderstanding.
And remember when you go to someone else's big fancy wedding - it doesn't prove anything at all about how much they're loved, or who will stay the distance.