Fair point.
- A wife is a woman who you sleep with on the understanding that she is committed to you for an indefinite period of time (even if you think divorce is permissible, that's not the plan, your understanding is that the two of you are a thing for as long as possible if not forever).
- A prostitute is a woman who you sleep with on the understanding that you are paying for her time for the next hour and she is giving you no commitment whatsoever beyond that time on the clock.
The difference is about intent. There is no difference regarding "one flesh" - sex creates a "one flesh" bond, whatever that is, so both situations create a "one flesh" bond. "One flesh" is identical in both circumstances. You cannot recognise the difference if you are unwilling to look beyond "one flesh". You might as well stand beside a car or a tractor, staring at the engine, and say "I can't see how these vehicles are different, because a vehicle is a thing with an engine, and they both have engines, so they're both the same" - while refusing to take your eyes off the engine and see any other parts of the vehicle.
And this then shows us the difference between sex with another man's wife, and sex with a prostitute. Sex with another man's wife is sex with a woman who
is committed to another man. Sex with a prostitute is sex with a woman who
is NOT committed to another man. The commitment / intent makes the difference.