third wheel
US /ˈθɜrd ˌwil/
UK /ˈθɜrd ˌwil/

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.