Husband and wife become "one" only in the same way light, heat and other things come together to constitute the one flame, yet are distinct. The husband and the wife are still distinct. Just as the Sender and the Sent are distinct from one another, by definition.
Analogously, the Father, Son and Holy Ghost are most certainly distinct in Scripture (e.g. one sends the other; submits their human will to the other, in the case of Jesus Christ; one recieves revelation or truth from one and conveys it to us, etc.). Yet if there is only one God (inarguably the teaching of the Old and New Testaments), then quite clearly these Persons (for they will and can be sinned against unto damnation, and speak messages, and make commands, and know all things, etc.) must somehow—God being ineffable—be one and the same God.
It is a logical fallacy (and thus an insufferable falsehood) to conflate two things in union with one another: union implies distinction in the first place (else what two things are in union?)
Unitarians who claim 'echad' (one in Hebrew) in fact means 'Unitarian' or 'Unipersonal' rob it of its clear context: a counter to the idea of polytheism (or, many-God-ism).
There are a few fundamental meanings for the word 'one:' one as in family (kinship, familial relationship); one in purpose, or agreement; or one as in an abacus (one counter, not two counters, etc.).
Which of these do they say God meant He is "one"? Clearly in the context it was said, it was a repudiation of idolatry, or polythiesm, or henotheism (YHVH, but others on the side, too).
We see Trinitarian formulae all over Scripture, e.g:
Matthew 28:19 (DRB)
Going therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.
1 Peter 1:2 (DRB)
According to the foreknowledge of God the Father, unto the sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace unto you and peace be multiplied.
They make God a ventriloquist, claiming Jesus was not talking to His Father, but Himself on the Cross, or saying He was one with Himself, instead of with the Father. Saying He came forth from Himself and into the world, instead of came forth from God, and thus is God. That He has Himself for His own Father, instead of He has God for His Father.
It is absolutely ludicrous, and, as said, a fallacy, to claim that the husband and wife are literally one person.