The phrase 'most lonely' is correct and usable in written English.
You can use it to describe a feeling of extreme loneliness or to emphasize how lonely someone is. For example, you could say, "He felt the most lonely he had ever felt in his life."
And out of everybody I have probably been the most lonely.
NC: It was the most lonely bit to perform when people weren't laughing.
Elsewhere, she notes, "Like most lonely women, like most women of all kinds, Margaret Dagemen had an imaginary lover….
Eldertainment seems like a way of exploiting society's most lonely and desperate and giving money and experience to the most advantaged and educated of students.
Amanda had three mobiles (that I knew of) and spoke to people from six in the morning to 1am the next day, but I think she will look back at this period as the most lonely in her life.
I have realized that Antarctica itself is a team sport, and living in the most lonely and isolated place on Earth does not necessarily mean that you are alone.
"I don't know exactly what I'm trying to say, I guess, but she came to my house the other night, bing-bong, most likely lonely for her boy, I'm thinking.
They're often a single isolated object; the most extraordinarily lonely still lifes imaginable.
So we looked at groups of soldiers who had come home, one of the most chronically lonely groups of people, and we went through all the available interventions.
The most recent Lonely Planet guide to India notes that tourism has been recovering slowly in the region but advises checking the security situation.
Just as the most successful lonely hearts go to the apps with the highest-number of potential suitors, so should graduates also head to where the most job opportunities are.
