You're texting about certain person of interest? (6)
I believe the answer is:
usurer
'person of interest?' is the definition.
(moneylender charging excessive interest)
'you're texting about certain' is the wordplay.
'you're texting' becomes 'ur' (informal spelling of 'you're' eg in text messages).
'about' means one lot of letters goes inside another.
'certain' becomes 'sure' (synonyms).
'ur' going around 'sure' is 'USURER'.
(Other definitions for usurer that I've seen before include "He takes much interest" , "One who charges undue interest" , "Extortionate lender of money" , "Loan shark" , "Grasping money lender" .)