The only friend dad has left? (3)
I believe the answer is:
pal
'the only friend' is the definition.
'pal' can be an answer for 'friend' (pal is a kind of friend). I am unsure of the 'the only' bit.
'dad has left?' is the wordplay.
'dad' becomes 'pa' ('pa' can be a synonym of 'dad').
'has' says to put letters next to each other.
'left?' becomes 'l' (common abbreviation).
'pa'+'l'='PAL'
Can you help me to learn more?
(Other definitions for pal that I've seen before include "Friend (colloq.)" , "China" , "Close friend" , "Bud" , "Buddy, chum" .)