Shiloh,
You have made some interesting assertions but which have very good answers.
How about if we both agree to answer whatever question the other asks?
So whatever question you ask, I will answer with a yes or no, if required, before presenting any reason etc.
If agreed, then you also will grant me the same respect.
Concerning betrothal, yes they were regarded as husband and wife by betrothal, the word "married" was also used, but everyone knew they had not become joined in marriage. So it is a mute point to make since Jesus defined what that situation is under which God has joined together that man is not to put asunder. It is that situation where a leaving and cleaving has occurred, where they are completely married living with one another. In the case of the divorce-for-fornication-in-betrothal explanation, the exception clause jumps to touch on that entirely different kind of divorce even though the topic of discussion, as established in Matt 5:31, is definitely the other normal post marital divorce. So in that case, (understanding that the the exception clause pertains to a divorce that DOES NOT put asunder what God has joined together), then everything falls into place:
In Matt 5:31,32, she is not caused to commit adultery by being put away for fornication while betrothed. Obviously because she has not ever been joined in marriage (she doesn't qualify for the status of "what God has joined together, let not man put asunder"). We see the same practical accommodating effect in Matt 19:9; he does not commit adultery by marrying another after that kind of divorce, for the same reason; he is still single not having graduated to having left and cleaved to his wife.
Please ask questions and I will do the same. By committing to answer each others questions, progress can be made in this discussion. If by your questions and answering my questions I discover and realize I am wrong, then I will very gladly admit that and be thankful for a better understanding. I trust you also have the same heart.
Concerning what I said above concerning the exception clause jumping to something other than what was the topic of discussion:
Would you like to see an example of a grammatical parallel where we have a sentence that functions after the same format of Matt 5:31,32 and where the exception clause jumps to what is NOT the topic of discussion?