There is something in the makeup of man that desires companionship. God said so right from the very beginning. "And the LORD God said, It is not good that the man should be alone; I will make him an help meet for him (Genesis 2:18)." The words "help meet" are one word in the original Hebrew. "Meet" in old English in this context means suitable, appropriate, or right. To have good companionship is all these things. Marriage is the closest relationship people can have with each other, but there are also others that can be "meet" and helpful. However, the Bible also makes it clear that not all relationships are right. The book of Proverbs speaks on this quite a bit. There are many examples in the Bible about good people associating with bad people and suffering for it. Good king Jehoshaphat kept making alliances with the evil kings to the north and their relatives, and he paid the price in his life and in the lives of his descendants.
There is a longing in the heart of man for relationship, for someone to share experiences with. "Two are better than one; because they have a good reward for their labour (Ecclesiastes 4:9)." When this need is unmet, people experience loneliness. This can have a powerfully negative effect. Studies have shown that babies who are not held and nurtured can actually die. God did not make us to be islands, as the poet John Donne pointed out. People attempt or commit suicide over loneliness. If we do not want to succumb to its draining and destructive influence, it is up to us to take action. "A man that hath friends must shew himself friendly...(Proverbs 18:24)." If we willingly shut ourselves off from others, we have no one else to blame for it. Loneliness is not usually caused by a lack of other people. It is caused by self-imposed isolation. You can be in a crowd of thousands and be lonely. We have to choose to do something about it if we want out.
On the other hand, you can be completely isolated from others and not be alone. What is the difference? It is having a relationship with God. When your desire for relationship is satisfied by God, you will never be alone. That does not mean we should not seek to have any meaningful relationships with others, but it does mean we never have to succomb to the destructive influence of loneliness. 2Corinthians 6:14-18 speaks of separating ourselves from those who would influence us to do evil and at the same time finding our heavenly Father readily available to us. You can always pray and have access to Him. You can always open you Bible and have His word fill your heart and mind. You can go to church and have many brothers and sisters.
Jesus Christ showed us this in His life and teaching (Matthew 12:46-50, Matthew 19:29, John 16:32). Imagine what it must have been like to be Jesus in His humanity. The very people He came for rejected Him (John 1:10-11) and called for His brutal torture and murder although He had done nothing but love them, teach them the truth, and heal them. Even His own disciples often did not understand Him. They failed Him at His hour of greatest need (Matthew 27). They did not understand the plan of His death. They fell asleep while He was praying great drops of blood. They forsook Him when He was arrested. Apparently John was the only apostle at the cross. Yet Jesus said He was not alone because the Father was with Him.
Sometimes we may not be physically alone, but we can be spiritually or emotionally. Sometimes this is even the will of God. There are parts of our journey with God that we must walk alone. There can people around us supporting us, encouraging us, and praying for us. Yet they cannot go to that place God is taking us to with us. Abraham, Moses, David, Elijah, and Paul are examples. When Jesus told Peter he was going to have to die for his faith, Peter looked at John and asked Jesus what he was going to have to do. The Lord told him not to worry about that, but to follow Him (John 21:18-22). We need to focus on the path God has for us, and stop comparing ourselves with others, because that is not wise (2Corinthians 10:12). Depression, which is the sister of loneliness, comes when we think our lot in life is unfair and too heavy, and nobody understands or cares. It seems like there is no solution. We will never understand everything in this life, but when we are in the presence of God, we can have a taste of heaven now, and the shadows of loneliness can flee. God will also send people to be a "help meet" for us. We don't ever have to let loneliness rule our spirits, emotions, or actions. We can overcome it through the Lord Jesus Christ.