Trinitarianism developed some centuries after the time of Jesus. It did not appear in the Bible although a trinitarian phrase was introduced into 1st John 5:7 in the 15th Century and found its way into the King James Version. (It does not appear in later translations of the Bible.)
A valued friend of many years remarked once that the Trinity is a beautiful metaphor, but a terrible dogma. By that he meant that, like so many dogmas, it has proved to be a source of conflict, some of it terrible conflict.
John Calvin had Michael Servetus executed for refusing to believe in the divinity of Jesus. A more serious and epoch making problem came with Mohammed's refusal to accept what he saw as a polytheistic religion, leading to a new religion that shows signs today of overtaking Christianity numerically.
The trinitarian doctrine of course was sanctified and made compulsory by Constantine with the Council of Nicea.
The statement of the Trinity that I can best live with comes from the pen of Howard H. Brinton on page 18 of Friends for 300 Years:
"God is One. He becomes manifest in various ways. In the O.T. he appeared as Father, in the Gospels as Son, and since the Gospel days as Spirit, revealing his will in the hearts of those who heed His voice." (The latter has sometimes been referred to as The Everlasting Gospel.)