I remember sitting in on a Missions class while I was in California, a few months before moving to Montana. Our instructor was pointing out the fact that God had done amazing and extraordinary things through Paul. I couldn't agree any more with him; Paul planted many churches, ministered to the body of Christ, loved on the body of Christ and the church in general loved him. God had even used Paul to write the majority of the New Testament and some would credit him as the guy who told Luke the story of Jesus, a story Luke would pen and distribute to his master Theophilus, a story that eventually landed into our hands today. No doubt God had done amazing things through Paul, but we see that even as God was using Paul, it appears that he had a war with loneliness which was far more evident at the end of his life.
While Paul was in prison, he wrote to Timothy telling him to come quickly. Paul also went on to tell Timothy that Demas, Crescens, and Titus had left him, telling Timothy that only Luke had stayed with him. Imagine the guys/girls you served along side with for years, people you have grown to love all of a sudden leaving you. So much time was invested in building a strong friendship while serving together yet they drop the relationship and give up on you.
I was warned before coming to Montana years ago (and I am so glad), that I would have my wars with loneliness just as Paul did. That the friends I would have expected to keep in contact wouldn't, and when I return for a visit there would not be any welcome back banners waiting but very brief and quick hellos and goodbyes. This is one of the major things my instructor would underline and bold while teaching the class, The Missionary's Loneliness, using Paul as the example, he couldn't have been any more right.
What is important to keep in perspective is that loneliness is a feeling. Some feelings are good but some feelings are unhealthy and dangerous. Some feelings are traps in disguise set by the devil as he aims to pull you down and hold you back from what God would like to do through you.
I believe that although Paul felt lonely, he remained focused. Soon after he wrote this letter, Paul was escorted to the chopping block and put to death. I would have a hard time believing that he allowed himself to get killed because he was depressed and lonely, that he believed life wasn't worth it anymore because his friends left him. He remained focused and died for the best cause; standing firm in faith in Jesus Christ.
Paul was a missionary on steroids, and if God had called us out to a strange place to do our part in getting work done for Him, then like Paul we must remain focused. And when those times of loneliness come; the missing of your friends and family stuff, the thinking of the good ol' days back home.. we must stand firm and remember that God is good, and His plans always work out for the good to those who love Him.
So to be a lonely missionary is normal, it is not a sin, it's not crazy. Paul a man mightily used by God felt it. But God was always with him and would get him through it and keep him going. Paul did the work he was called to do because he leaned on Him. Us lonely missionaries could learn from that.