Subject + 是 + 孤单 + 的
孤单 (gūdān) is an adjective meaning "lonely" or "alone." It describes a feeling of solitude or isolation, often with an emotional undertone of sadness. It can be used as a predicate adjective after 是 (shì) or modified by degree adverbs.
一个人住在外面,有时候会觉得很孤单。
Yī gè rén zhù zài wàimiàn, yǒu shíhou huì juéde hěn gūdān.
Living alone outside, sometimes you feel very lonely.
自从朋友搬走以后,她变得越来越孤单了。
Zìcóng péngyou bān zǒu yǐhòu, tā biàn de yuè lái yuè gūdān le.
Ever since her friend moved away, she has become more and more lonely.
别担心,有我在你不会孤单的。
Bié dānxīn, yǒu wǒ zài nǐ bù huì gūdān de.
Don't worry, with me here you won't be lonely.