This subject is one in which it should be acknowledged that "Trinity" is not found in the Bible, but there are verses which imply it. Non-trinitarianism was found in the early churches, and the trinitarian view was not firmly established until Constantine forced its acceptance, and even then there was dissent.
However, I think, as I and others have shown, that there is Biblical evidence for the Trinitarian position.
God, in His own timing, took millenniums to reveal His Essence to us, speaking mainly to this subject in these last days through His Son Jesus Christ and the Apostles. God is not taken by surprise that human beings would have a difficult time understanding God. The Trinity is something that took some time to understand mostly due to limited revelation, but from the very writings of Moses, since around 1400BC, God revealed to mankind that He was a Plural Being, when He said "Let us make man in our image". This does not define a Trinity at this time, but it does define a plurality in God that cannot be denied. Well, not honestly denied anyways. For this to be denied is simply one looking for an excuse not to see it.
Not sure "imply" is a correct observation. There are passages which "declare" the Father is God, the Son is God and the Holy Spirit is God, and although they are all God the scripture declares they are One God and not three different competing gods. It is certainly a mystery, yet it is what the scripture declares. Humanly we may not understand how this can be, God is God, we take Him at His Word.
Constantine had nothing to do with developing the belief in the Trinity. You might have gotten that from people who have read the da vinci code book. Tertullian coined the words "Trinity" and "person" and explained that the Father, Son and Holy Spirit were "one in essence - not one in Person. And this was written within 100 years after the Apostles had finished the cannon of holy scripture. No one can be forced to accept the Trinity teaching, no more than one can be forced to be a Christian.
We see through early non-scriptural Christian writings that the Trinity was seen and understood shortly after the Apostles finished the scriptures.