là le problème est que prestion ne parle plus, t'es plus à ça près tu peux toujours tester 
http://steamcommunity.com/app/377160/discussions/0/496881136913298034/#c496881136913440652
I've had this issue with him not giving the companion dialogue after Taking Independence too, I believe I might have just found a console fix for it.
Open console
Select Preston
removefac 00075D56
Faction 00075D56 is apparently some kind of artificial state faction which is used to temporarily block characters from being recruited as companions, like during a quest or something. I think Bethesda forgot to remove him from it after Taking Independence finishes.
Removing him from the faction via console seems to restore full companion functionality. As with everything related to the console, use with caution and make sure to make a separate save before trying.