Meaninglessness happens when the one thing that one has put his or her affections on has ceased to be. And that reality of affections ceasing to be something attainable becomes desire. And that desire is the reality that our affections will never become something possible and thus erodes perspective. When perspective has ceased meaning it becomes nothing and when nothing becomes the definite reality of the present it births meaninglessness.
And meaninglessness soon becomes the perspective that now lives and breathes on the landscapes of possibility but possibility is never seen as a reality because perspective has been widened. The feeling of meaninglessness is when one sees everything but the difference is the person ceases to feel.