Married, following which regularly surlier and cross (4)
I believe the answer is:
mule
'cross' is the definition.
(a mule is a cross of a donkey and a horse)
'married following which regularly surlier' is the wordplay.
I cannot really understand how this works, but
'married' could be 'm' (abbreviation, e.g. in genealogy) and 'm' is located in the answer.
The remaining letters 'ule' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'and' is the link.
Can you help me to learn more?
(Other definitions for mule that I've seen before include "Backless slipper" , "Proverbially stubborn animal" , "Equine hybrid" , "on foot?" , "Donkey-horse hybrid" .)