I would say the money you saved for a ring could buy some new glass?
Ahaha, yes. I thought the same thing reading the OP.
Also, OP: regarding the relationship falling apart days before proposing... that's actually really common in my experience, and you shouldn't let that aspect of it get to you (I know when that happened to me, that was a particularly annoying detail). Girls know they are about to be proposed to more often than not, and if the relationship has problems, that's a great time to stop it before it escalates to an even more awkward breakup at the moment of proposal. So probably not very coincidental at all. You simply forced her to action, which is good, because action is better than suppressed misgivings.
Otherwise, I dunno. The only useful "getting over breakups" advice that I have received and used is to cut yourself off from any easy opportunities to wallow in memories.
1) Either destroy/delete reminders of her, or if you feel you may want them someday, then ship them to a family member to hold onto out of your reach until later.
2) Block her on facebook and so forth (if it was a somewhat amicable breakup, then tell her why you're doing this first so it doesn't come across as petty. Explain it is temporary to help you move on, etc.).
3) Don't fight over any friends that are likely to be more devoted to her.
4) Do any leftover item exchanges or whatnot as soon as possible and as all-at-once as possible to remove any lingering loose ends.
5) Talk about it once, maybe, with her, after plenty of time to cool down, if closure is really needed. But ideally not even that, and certainly nothing more than that for at least a couple months or more.
Cutting all the cords will make the time shorter to get over it. But it's still just gonna be some passage of time. Gotta feel crappy for awhile, no way around it.
Rebound relationships also help, if you're the sort of person who can stomach such a thing. If so, please be completely honest with the rebound person (there are plenty of people who won't care and would be happy to serve that role), and call it off if you feel they have unrealistic expectations anyway. I can't handle this, personally. It helps at first, but then I'm too damn sappy to go through with much of any relationship that I don't intend to be long term, so it kinda backfires. If that's not a problem for you though, it could work great.