Well, I can sympathise a little, even though I haven't been in that position myself.
When your child is an adult you can't help wanting a lovely life for them, whatever that means to you. And when they find a partner you like, I can imagine wishing they would make it permanent, even though you KNOW you shouldn't, it's irrational, and so on. There is also the other side of it, ie friends with children marrying, and perhaps you feel envious and don't want yours to be left behind.
I don't think there is much you can do except say nothing, be happy whatever they do, and talk about it somewhere else, though.
I know someone who is very keen for her children to marry. I wish she'd chill a bit because the choices they have made are not going to be good, at least for one of them. But she's certainly showing a huge urge to see them married, regardless of how suited they are - so, very different from you in that regard.
However - I do think she is driven by what other people's children are doing, to some extent. A few weddings have been taking place.
It's not easy, but maybe you can just admit you feel this way (nothing wrong with feelings) - but also admit that it's not up to you what happens. Then do your utmost to look outwardly unconcerned, and turn your mind to fun and enjoyment in your own life.