Meaning of the word "the tongue always returns to the sore tooth" in English

What does "the tongue always returns to the sore tooth" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

the tongue always returns to the sore tooth

US /ðə tʌŋ ˈɔːlweɪz rɪˈtɜːrnz tuː ðə sɔːr tuːθ/
UK /ðə tʌŋ ˈɔːlweɪz rɪˈtɜːnz tuː ðə sɔː tuːθ/
"the tongue always returns to the sore tooth" picture

Idiom

one cannot help but return to or think about a subject that is painful, troubling, or embarrassing

Example:
He keeps mentioning his failed business; I guess the tongue always returns to the sore tooth.
Even though she tried to move on, the tongue always returns to the sore tooth and she kept checking her ex's social media.