Loosely using the term marriage because marriage as the concept we understand, I don't remember actually being defined in the bible as we use it. It mostly being inferred as contextually a single word descriptor for exclusive sexual access, authority/headship, and ownership of a woman by an individual man, one man at a time. If sex = marriage then what about slaves and concubines? As they are not "ishah", they have their own descriptor words, sex with them however is also inferred as permissible or carry exceptions to the adultery punishment, but does not instantly raise them to "wife status". The only time we ever see sex = forced marriage is in relation to a seduced/raped virgin who is unbetrothed, which even that scenario contains a void option, that is only available to the father, meaning her change of status it is not immediate nor a requirement. The text is clear there is still an order of operations, he must pay the bride price first, then she shall be his wife. From this and other things we can infer the father is the final authority before she is transfered to her husband.
But how is this scenario handled when there is no authority? If the father is dead...does it become an exception? The scenario not an unrealistic one, especially during biblical times....must they be married? Who does he pay the bride price to? Because she is no longer under her fathers authority is she like a widow or divorced woman without a head who carries their own accountability and can make their own final decisions? Or as an orphan does she fall under the passages for orphans? Covered by The Most High directly, not to be trespassed against lest his wrath be reaped.
Then there's the virgin betrothed woman who CAN commit adultery, in her sexless status. So we know betrothal is a status at least equal to "marriage" because violation carries the same punishment as a consummated marriage and we know adultery as a classification is only ever applied once a woman belongs to a man and yet the exception of a betrothed slave cannot be ignored, which I would also note it does not state her as a virgin, nor does it state either parties intent or consent. see Lev. 19:20-22.
If we drop the term marriage entirely, what are we left with to define a womans status other than the one flesh description as an act which contextually refers to consummation every where I can remember, as the last step in the series of marital events, never mentioned without the series, except in the prostitute reference of Corinthians. Still lacking a solid definition for one flesh as its first use is both equal to "go into or knew her" but also the bearing of fruit from that action so it contains a double meaning, how is it to be applied to the unbetrothed from above?
Considering the woman at the well (where many infer without it being stated as to why she is attributed to having multiple husbands, is she a prostitue, a concubine, a divorced woman, or an adulteress?) she has had 5 husbands and the man she has now was not her husband, we have no way to know if this is infering a one flesh union with the 6th man or just a living situation and with no real clarification as to her current status or how she came to be in this situation, we can only infer from the response of the townsfolk and the disciples that she probably wasnt of a shameful status, which means probably not a prostitute or adulteress.
There are just so many holes and inconsistencies in the sex = instant marriage argument...