This is the essential nature of loneliness. We often equate loneliness with aloneness. So, when we are alone, we find someone to be with and this assuages the pain, but it is temporary. For the relationship is not permanent, nor did it seem to provide what it promised. The fear of loneliness is repressed, but not dispelled.
Nothing is permanent.
Again and again our teachers point to this central precept. Look yourself and meditate on this. Nothing we build stands for longer than a few years. The cycle of time is endless, repeating patterns of seas and mountains and the burning galaxies, until even the patterns change and the fires go out. In our heart of hearts we realize this, but it is a difficult insight to dwell upon.