Okay, y'all made me look up some caselaw.
Georgia has a public policy favoring marriage of single adults.
A promise to marry can be a common-law contract, and the courts can award damages (including the costs of the no-longer-needed wedding).
And the actions of one fiancee that harm the other can be a tort action, too.
There isn't a lot of law on this subject, but enough to know it's a valid cause of action.
This is the seminal case in our lifetimes on this subject, since it's from the Supreme Court of Georgia.
Thorpe v. Collins, 245 Ga. 77, 78(1), 263 S.E.2d 115 (1980).
Even though the actual holding of that case went the other way, finding that there is no enforceable promise to marry when the person making the promise was already married, and added a condition precedent that he be divorced or widowed before he would marry the other woman.
I stand corrected.
I knew promissory estoppel would apply to a promise that could have been the subject of a contract but wasn't-- it was just a promise that was reasonably relied on to the detriment of the promisee. But I did not think that promissory estoppel would apply where the promise was such that it could not have been made in contract because it was contrary to public policy, like for example a promise to drive the getaway car for a team of bank robbers. If the getaway driver abandons his robbing crew and they all get caught and sue him, they cannot recover under any theory, period, because the agreement/ promise was about illegal activity. I thought that a promise to marry could not be enforced over someone's objection, and therefore no damages could be ordered by a court. Wrong.
(Another tidbit of information I am likely to never need again, ever, for as long as I practice law!)