@rosetonightplease - I've been where you are. Kind of. Dh was married but separated when we met. We ended up with house and 2 babies before his divorce was finalised.
The day his decree absolute arrived we hot footed it to the registrars office, gave notice and got married 30 days later! (You have to have 28 full days notice of intention to marry). We've been together 13 years, married for 8. I love him to bits.
You seem to be striving for perfection and that way madness lies! Yes it would be wonderful if he had a spare 5k to drop on your perfect ring. But that's £5000 you could also spend on so much else when you are also planning a family.
He has bought you a ring. He has spent time considering what you would like and chosen this one. But because it's not the ring you want and he knows it, he has said it is a 'promise' ring, a promise of engagement.
When you talk that you already have a 3k ring and a Rolex, I can see why he feels like he has to try and keep up with the standard you have set.
For context, dh sold his Rolex watch to pay for our first baby's things and some extra furniture we needed, and we didn't go for top of the range either.
It doesn't actually matter how long you've been together but it does matter that you seem to be so materialistic when your dh can not afford to be so spendy. That is the sort of imbalance which will end up causing problems down the line.