When Jesus was a man on Earth, did he cease being God in Heaven? Was there a Trinity prior to the birth? Were there two

[muriel_volestrangler]

18. There's a lot of influence of Platonism, both in John 1, and the development of the "Trinity" by Tertullian

about 150 years later.

A direct influence on second century Christian theology is the Jewish philosopher and theologian Philo of Alexandria (a.k.a. Philo Judaeus) (ca. 20 BCE–ca. 50 CE), the product of Alexandrian Middle Platonism (with elements of Stoicism and Pythagoreanism). Inspired by the Timaeus of Plato, Philo read the Jewish Bible as teaching that God created the cosmos by his Word (logos), the first-born son of God. Alternately, or via further emanation from this Word, God creates by means of his creative power and his royal power, conceived of both as his powers, and yet as agents distinct from him, giving him, as it were, metaphysical distance from the material world (Philo Works; Dillon 1996, 139–83; Morgan 1853, 63–148; Norton 1859, 332–74; Wolfson 1973, 60–97).
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Justin Martyr (d. ca. 165) describes the origin of the logos (= the pre-human Jesus) from God using three metaphors (light from the sun, fire from fire, speaker and his speech), each of which is found in either Philo or Numenius (Gaston 2007, 53). Accepting the Philonic thesis that Plato and other Greek philosophers received their wisdom from Moses, he holds that Plato in his dialogue Timaeus discussed the Son (logos), as, Justin says, “the power next to the first God”. And in Plato’s second letter, Justin finds a mention of a third, the Holy Spirit (Justin, First Apology, 60). As with the Middle Platonists, Justin’s triad is hierarchical or ordered. And Justin’s scheme is not, properly, trinitarian. The one God is not the three, but rather one of them and the primary one, the ultimate source of the second and third.
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Another influence may have been the Neoplatonist Plotinus’ (204–70 CE) triad of the One, Intellect, and Soul, in which the latter two mysteriously emanate from the One, and “are the One and not the One; they are the one because they are from it; they are not the One, because it endowed them with what they have while remaining by itself” (Plotinus Enneads, 85). Plotinus even describes them as three hypostases, and describes their sameness using homoousios (Freeman 2003, 189). Augustine tells us that he and other Christian intellectuals of his day believed that the Neoplatonists had some awareness of the persons of the Trinity (Confessions VIII.3; City X.23).
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Under the influence of Stoic philosophy, Tertullian believes that all real things are material. God is a spirit, but a spirit is a material thing made out of a finer sort of matter. At the beginning, God is alone, though he has his own reason within him. Then, when it is time to create, he brings the Son into existence, using but not losing a portion of his spiritual matter. Then the Son, using a portion of the divine matter shared with him, brings into existence the Spirit. And the two of them are God’s instruments, his agents, in the creation and governance of the cosmos.
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Despite these fundamental differences from later orthodoxy, Tertullian is now hailed by trinitarians for his use of the term “Trinity” (Latin: trinitas) and his view that it (at the last stage) consists of three persons with a common or shared “substance”.

https://plato.stanford.edu/entries/trinity/trinity-history.html