See my post #132. The allusion is found within the confines of the last several centuries and perpetrated by men in our “Christian” culture with a predisposition and proclivity to both see and allude to sex whenever possible.
The definitions and usage of the word cleave, especially in the era of the translation of the KJV was specifically to lay hold on or to bring alongside rather than to “split” as in a piece of firewood or spread as in a pair of legs. It’s usage, definitions and the words substituted for it (as Ephesians 5 does with the word joined) Scripturally do not support its association with sex either in allusion or implication. One of the more humorous examples is Acts 8:29
Then the Spirit said unto Philip, Go near, and join thyself to this chariot.
IF kallao (cleave, join) is a euphemism for sex, then
Then the Spirit said unto Philip, Go near and have sex to this chariot.
This is just one of many examples, every one of them utilizes and defines kallao as being joined either by association, covenant, employment, or ideology.