Live with a warm-hearted European (3)
I believe the answer is:
are
'live' is the definition.
('they live' means 'they are')
'with a warm-hearted european' is the wordplay.
'with' means one lot of letters go next to another.
'hearted' says to take the centre.
'european' becomes 'E' (abbreviation e.g. EU).
The centre of 'warm' is 'ar'.
'ar'+'e' is 'ARE'.
(Other definitions for are that I've seen before include "Is, in the plural" , "Era (anag.)" , "Unit of land measure equal to 100 square metres" , "(We/you/they) exist" , "Exist; square measure" .)