If there is only one God and no trinity where its three persons in one, why does the bible constantly talk about the son and father's love?

You do not understand our Christian Bible or our Religion because of the Below.

1 Corinthians 2:14

But A Natural Man Does Not Accept The Things Of The Spirit Of God, For They Are Nonsense Or Foolishness To Him, And He Cannot Understand Them Because They Are Spiritually Appraised. (Comprehend)

Corinthians 1:18-19. 2 Corinthians 4:3-4,6

"Words simply can't describe and man certainly cannot comprehend it..." This is what Christians would like us all to believe about their man-made doctrine - TRINITY = A MYSTERY!

The FATHER is the SENDER = SEPARATE!

The SON is the SENT = SEPARATE!!

Even Jesus attested to the above facts in numerous verses of the New Testament.

(1) John 17:3 - Now this is eternal life: that they know you, the ONLY true God (and SENDER), and Jesus Christ (the SENT), whom you have SENT.

(2) John 8:42 - Jesus said to them, "If God were your Father, you would love me, for I have come here from God (the SENDER). I have not come on my own (the SENT); God sent me.

But no amount of telling will do it for those who are determined to follow their true deity to damnation.

Son of God = Will of God = Word of God = Mind of God = Thought of God = Image of God = Desire of God = CHRIST = GOSPEL = FIRE, etc.. The Holy Spirit is like ever-present energy from God. The Holy Ghost is incapable of disobeying the Father: Christ the Son can disobey His Father, but he doesn't.

There is one God, one Faith, One baptism. God our Father in heaven, came down in human form as Jesus and when Jesus returned back to heaven, left us with his Holy Spirit to comfort, teach and guide as promised. When we see God the Father who is Spirit, we will see him as Jesus (God-Man). Jesus is God in the flesh. It is all relational. Words simply can't describe and man certainly cannot comprehend it very well but by faith we believe.

Only one Almighty God, and many gods.

Old Testament non-trinitarians are simply wrong, that's what it means.

there is only one God and no trinity in Islam, JW, and Atheism

That is only TWO-no trinity :)