I've suspected loneliness is the "human condition" since I was a teenager. To me, it's not a sad or scary thought - it's just a thing that we have as part of our humanness. It might actually be liberating to remind ourselves that feeling lonely is natural and normal. You can't patch that feeling up with a partner or a family or a dream job or social life. You can, at best, only distract yourself from it for a while.
This video by Hannah Jacobs does a great job addressing aloneness ... though I don't agree that being in love is an illusion. You can be lonely and in love at the same time and the one feeling is just as real as the other.
Because we humans are just skin and bones and brains full of contradictions.