third wheel

US /ˈθɜrd ˌwil/
UK /ˈθɜrd ˌwil/
"third wheel" picture
1.

terzo incomodo, ruota di scorta

a person who is in a situation with two other people who are romantically involved or who are very close friends, making the third person feel awkward or unwanted

:
I felt like a third wheel on their date.
Mi sentivo come un terzo incomodo al loro appuntamento.
They're always together, so I often feel like a third wheel when I'm with them.
Sono sempre insieme, quindi spesso mi sento un terzo incomodo quando sono con loro.