The article in U.S. Catholic didn’t seem all that scholarly. The authors assert that the idea of betrothal follwed by marriage has been accepted by the Church in the past. Well, of course.
It still is.
They also state that sex following betrothal was considered “marital” sex, but they didn’t provide any historical evidence to back up that assertion.
If in fact, sexual intercourse following betrothal is marital sex, then the parties are really married at betrothal, and the ultimate wedding is just a nice ceremony to top it off and get gifts.
It also follows that breaking a betrothal would be the equivalent of breaking a marriage–i.e. not allowed.
If sexual intercourse following betrothal is not marital sex, then it is fornication. And the Church has always condemned fornication.