In the Bible, does it really say that if you don't believe in God, you will go to Hell?

"Whoever believes in him is not condemned, but whoever does not believe stands condemned already because they have not believed in the name of God’s one and only Son...Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God’s wrath remains on them. "

John 3:18-36

"But the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liars—they will be consigned to the fiery lake of burning sulfur. This is the second death.”

Revelation 21:8

Those are the best examples I could find. It is up to you to decide whether torturing someone for eternity for not believing something can ever be considered just.

Hope that helps!