We are not meant to be lonely. Or alone for a long time. Intimacy feels good, intimacy is a need, intimacy is a part of our neurological wiring. People are social, it is amazing, but even "self-sacrifice" is a part of our genetic programming. The evolution of humanity is due to its social development, part of which is intimate connections. Without social connection, we, as other animals would have still occupied the jungles of Africa.
An infant does not survive without caring adults, adults can survive isolation, but not without suffering, in fact "solitary confinement" is a torture.
"Whatever our individual sensitivity, our well-being suffers when our particular need for connection has not been met. Because early humans were more likely to survive when they stuck together, evolution reinforced the preference for strong human bonds by selecting genes that support PLEASURE in company and produce feelings of unease when involuntarily alone. Moreover, ..., evolution fashioned us not only to feel good when connected, but to feel secure. The vitally corollary is that evolution shaped us not only to feel bad in isolation, but to feel insecure, as in physically threatened." John T. Cacioppo & William Patrick "Loneliness"