Your reasons aren't great, tbh.
You sound like you're insecure and marriage will "fix" it.
The talk of wanting to be proposed to and most of all this focus on he married her but not me... that's not good reasons for wanting marriage.
Not even logical: not marrying a second time doesn't mean you don't like the second person as much. Could mean you simply learned your lesson - quite the opposite of preferring the first person!
It's fine if you definitely want marriage for good reasons, to say so. And if he doesn't it's fine for that to be a deal breaker for you.
But be sure on your motives for marriage.
TBH, it is such a meaningful legal contract, that I'm surprised that so many people marry a second time when they are past the having-children stage. Well - I'm not surprised at all by the 50% of the financially weaker parties. But the financially stronger? We are having a pre-nup (yes, I know it's not binding). I adore my fiancé and whilst we are married our money is pretty much one pot. But I've been divorced. I don't intend to give my assets up if I divorce again - which isn't statistically unlikely.
If marriage were purely a business contract, the stronger financial party's legal team would be saying "you what? Jog on!"
Are his reasons financial?
My fiancé and I had a very open and relaxed conversation about that.