...So my question is, can you be Christian if you don't believe Jesus or the Holy Spirit are God?
In some ways I understand the Trinity if I think of it in a certain way: That the Father, Jesus the Son and Holy Spirit are different expressions or modes or relations to one God. I am unsure whether that counts as the Trinity though....
Modalism is a heresy that arose in the Third Century; it's also called Sabellianism. It's an idea that is completely contrary to authentic Christian thought, as is the idea that Jesus and the Holy Spirit are not God.
The Council of Nicea specifically rejected these ideas, and through it and a couple of other Councils the Church formulated the correct view as
I believe in one God, the Father Almighty, maker of heaven and earth, and of all things visible and invisible. And in one Lord Jesus Christ, the only begotten Son of God, and born of the Father before all ages: God of God, Light of Light, true God of true God. Begotten not made, consubstantial to the Father, by whom all things were made....And in the Holy Spirit, the Lord and Giver of life, who proceeds from the Father and the Son, who together with the Father and the Son is to be adored and glorified, who spoke by the Prophets.
Consubstantial with the Father... of the same substance.
The Athanasian Creed says it this way:
And the Catholic Faith is this, that we worship one God in Trinity and Trinity in Unity. Neither confounding the Persons, nor dividing the Substance. For there is one Person of the Father, another of the Son, and another of the Holy Ghost. But the Godhead of the Father, of the Son and of the Holy Ghost is all One, the Glory Equal, the Majesty Co-Eternal. Such as the Father is, such is the Son, and such is the Holy Ghost. The Father Uncreate, the Son Uncreate, and the Holy Ghost Uncreate. The Father Incomprehensible, the Son Incomprehensible, and the Holy Ghost Incomprehensible. The Father Eternal, the Son Eternal, and the Holy Ghost Eternal and yet they are not Three Eternals but One Eternal. As also there are not Three Uncreated, nor Three Incomprehensibles, but One Uncreated, and One Uncomprehensible. So likewise the Father is Almighty, the Son Almighty, and the Holy Ghost Almighty. And yet they are not Three Almighties but One Almighty.
So the Father is God, the Son is God, and the Holy Ghost is God. And yet they are not Three Gods, but One God. So likewise the Father is Lord, the Son Lord, and the Holy Ghost Lord. And yet not Three Lords but One Lord. For, like as we are compelled by the Christian verity to acknowledge every Person by Himself to be God and Lord, so are we forbidden by the Catholic Religion to say, there be Three Gods or Three Lords. The Father is made of none, neither created, nor begotten. The Son is of the Father alone; not made, nor created, but begotten. The Holy Ghost is of the Father, and of the Son neither made, nor created, nor begotten, but proceeding.
So there is One Father, not Three Fathers; one Son, not Three Sons; One Holy Ghost, not Three Holy Ghosts. And in this Trinity none is afore or after Other, None is greater or less than Another, but the whole Three Persons are Co-eternal together, and Co-equal. So that in all things, as is aforesaid, the Unity in Trinity, and the Trinity in Unity, is to be worshipped. He therefore that will be saved, must thus think of the Trinity.
Furthermore, it is necessary to everlasting Salvation, that he also believe rightly the Incarnation of our Lord Jesus Christ. For the right Faith is, that we believe and confess, that our Lord Jesus Christ, the Son of God, is God and Man.
God, of the substance of the Father, begotten before the worlds; and Man, of the substance of His mother, born into the world. Perfect God and Perfect Man, of a reasonable Soul and human Flesh subsisting. Equal to the Father as touching His Godhead, and inferior to the Father as touching His Manhood. Who, although He be God and Man, yet He is not two, but One Christ. One, not by conversion of the Godhead into Flesh, but by taking of the Manhood into God. One altogether, not by confusion of substance, but by Unity of Person. For as the reasonable soul and flesh is one Man, so God and Man is one Christ.
This totally eviscerates both Arianism and Sabellianism.
As to whether or not one can have a relationship with Christ while having false ideas about him, I'll just point out that gnosticism is a heresy as well. We're obligated to make sure that our intellect and conscience is well formed, but ultimately the question isn't
what knowledge did you have about Christ so much as it is
how did you respond to the knowledge God gave you? If our intellect and conscience are malformed because we wanted them to be, that's a problem because it involves a rejection of God.