By betrothal,
1) No one considered Dinah Shechm's woman post sex, they did consider him fornicating with her though, then agreed to intermarry.
2) Mary is divorcable by Joseph pre sex.
3) A raped woman is not the rapists, unless the father allows it.
4-6) And if she is already betrothed it is adultery, if she is in the city and doesnt scream it applies to both parties, if she does, then only the rapist is guilty. If she is in the country it only applies to the rapist.
6 scriptural references all contradicting sex = marriage. Betrothal (Aras) is pre Marriage (chathan), which is pre sex (Shakab see Mary above). Sex equaling marriage effectively invalidates fornication as a concept, because if sex alone = marriage you are left with only 2 outcomes, marriage or adultery. Please provide counter scripture.
I actually have a 7th reference, Exodus 21:1-6, again deals with the master giving the slave a wife. The male slave cannot take her from his master, she is the masters to give and her and any offspring remain the masters.
But if the slave had a wife to begin with she belongs to the slave. If a man lays with a slave woman who is betrothed to another that is a violation, though its punishment is not akin to adultery, nor its it called adultery, but its still fornication, as she is another mans, but she is not free.
Again we see the violation is based on her betrothal status, not her ownership status, nor her sex status.
8th! Note even with a warbride there is a procedure to be completed before she is a valid wife, you cannot just sex her down.