My religion clearly mentions that Trinity is not truthful and the Christians should not believe in it:
[5:73] Indeed they are disbelievers who say, Surely, Allah is none but the Messiah, son of Mary, whereas the Messiah himself said, O children of Israel, worship Allah Who is my Lord and your Lord. Surely, whoso associates partners with Allah, him has Allah forbidden Heaven, and the Fire will be his resort. And the wrongdoers shall have no helpers.
[5:74] They are surely disbelievers who say, Allah is the third of three; there is no God but the One God. And if they do not desist from what they say, a grievous punishment shall surely befall those of them that disbelieve.
The Holy Quran Arabic text with Translation in English text and Search Engine - Al Islam Online
This is what I understand from my religion; others could believe differently, in my opinion.