The idea that "Jesus was the Son of G-d in the sense of the first creation of G-d ... not that Jesus is G-d and I consider the Holy Spirit a Divine Energy, not a Person" is Arianism The major denomination still holding that view is the Jehovah's Witnesses, many of whom identify Jesus with an Archangel such as Saint Michael. The other major non-Trinitarian group in the U.S. are the Unitarian Universalists, who are more similar to the Sabellians who taught that the Father, Son and Holy Spirit are essentially synonymous .I'm among those few Christian Protestants who don't believe in Trinity [I think that Jesus was the Son of G-d in the sense of the first creation of G-d ... not that Jesus is G-d and I consider the Holy Spirit a Divine Energy, not a Person].
This said, it's evident that it's all about a theological debate. If we want to keep it on the historical layer we should wonder when Trinity became the dominant belief about the nature of G-d.
Now ... to defend the theological conception [which appeared only in II century CE ...] someone says that already in the Gospel of Matthew it was present.
Nice ... but where it's said that they are the same person?
There are various passages in the Bible that are taken to suggest the Trinity : use of the plural Elohim for God in Gen. 1:1; Jesus' statement John 10:30: "I and the Father are one"; 2 Cor. 13:14:The grace of the Lord Jesus Christ and jthe love of God and kthe fellowship of the Holy Spirit be with you all." , etc., plus the references by Jesus to sending the Holy Spirit; John 14:16-17). Matthew 28:19 (Go you therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit" . and 1 John 5:7-8 (“For there are three that testify: the Spirit, the water and the blood; and the three are in agreement") are passages most frequently used. Note, however, that the KJV translation of John 5 is more explicitly Trinitarian than others. We have similar statements by Clement of Rome, Ignatius of Antioch and Justin Martyr. But the connection wasn't made explicit. That seems to have begun in the second century by Theophilus of Antioch who writes of God, Logos and Sophia: and by Tertulian in the third century c.e., who defends the concept against Praxeas. Arianism was defeated at Nicaea in 325 c.e., Bishop Alexander of Alexandria and Athanasius leading the Trinitarian faction. Arianism was by no means dead. Constantine was baptised on his deathbed by an Arian, and Arianism was supported by Constantius II and affirmed in no less than Eleven Arian confessions by various councils of bishops. as late as 361 c.e. First Nicaea had little to say about the Holy Spirit, whose position was affirmed at the First Council of Constantinople in 381 c.e. Two years later, the formula of Constantinople was reaffirmed in a statement that was not contested by subsequent Arian decarations.