Former partner flexible about contact initially — it can be understood (10)
I believe the answer is:
explicable
'it can be understood' is the definition.
(something explicable can be understood)
'former partner flexible about contact initially' is the wordplay.
'former partner' becomes 'ex'.
'flexible' becomes 'pliable' (synonyms).
'about' indicates putting letters inside.
'initially' indicates taking the first letters.
The first letter of 'contact' is 'c'.
'pliable' placed around 'c' is 'plicable'.
'ex'+'plicable'='EXPLICABLE'
(Another definition for explicable that I've seen is " readily understood".)