Life partner gets fine - it's the severest of punishments for someone who's going to be late (5,7)
I believe the answer is:
death penalty
'fine it's the severest of punishments for someone who's going to be late' is the definition.
I can't tell whether this definition defines the answer.
'life partner' is the wordplay.
'life' becomes 'death' (death is a kind of life).
'partner' becomes 'penalty' (I can't justify this - if you can you should give a lot more credence to this answer).
'death'+'penalty'='DEATH PENALTY'
'gets' acts as a link.
Can you help me to learn more?
(Another definition for death penalty that I've seen is " Capital punishment".)