What does the Bible say about loneliness?

The LORD God also said, “It is not good for the man to be alone. I will make for him a suitable helper.”Genesis 2:18

It is not good for the man to be alone — said while everything is still good.

Turn to me and be gracious, for I am lonely and afflicted.Psalms 25:16

For I am lonely and afflicted. The word is used of himself, without apology.

“I have been very zealous for the LORD, the God of Hosts,” he replied, “but the Israelites have forsaken Your covenant, torn down Your altars, and killed Your prophets with the sword. I am the only one left, and they are seeking my life as well.”1 Kings 19:10

Elijah says he alone is left. He is factually wrong, and is fed and let sleep before being corrected.

God settles the lonely in families; He leads the prisoners out to prosperity, but the rebellious dwell in a sun-scorched land.Psalms 68:6

God sets the lonely in families.

Keep your lives free from the love of money and be content with what you have, for God has said: “Never will I leave you, never will I forsake you.”Hebrews 13:5

Never will I leave you — a quotation of a promise first made to Joshua.

Then Jesus returned to the disciples and found them sleeping. “Were you not able to keep watch with Me for one hour?” He asked Peter.Matthew 26:40

Jesus asks three friends to stay awake with Him, and they do not.