Maybe my experience is relevant. I was modestly frugal and trying to save more, but not focused as I am now, when engagement fever hit my life. Fiance then, (wife now) was a spender and not particularly materialistic but what she does want is the best. And she wanted a big pretty rock.
10K later and she (we) stared at that beautiful big thing for a few months, we marry, all is well, and now 3 years later she doesn't wear it because its just too blingy and it embarrasses her. It was a great lesson in opportunity cost as now we would love to have 5K of that to take a trip or max our Roth for the year or ???
Point is, be very thoughtful, because what you want now, can change drastically.
As an aside, I have learned a lot from my wife regarding spending--she sometimes seemed careless about it, but the attitude she has regarding money--that it is abundant and you can go get some if you need it, has been very valuable. It's an emotional shift that means I both make more, and combined with MMM tactics, save more. So if you need to spend a lot on a ring, so be it. Go get that money.