There are so many contradictions about him and his behaviour. Sometimes he acts like the perfect JW, and then it feels like I am actually talking to him for real...
Astute observation on your part and a critical one. It's something common to all cult members who undergo thought and behavioural control. It's commonly referred to as the "cult personality" v the "genuine personality".
The perfect JW is the cult personality. By questioning his beliefs for him, you typically invoke the cult-induced response and can actually inadvertently confirm his cult mindset. The "real him" is the genuine personality . . . and the level you need to communicate on as much as possible. The two personalities have buried conflicts . . . and so appealing to the genuine personality empowers it.
He will only successfully question his beliefs when the time is right . . . and you will need to be very careful if prompting him to do that. Once that cult defence is induced toward you personally . . . you've burned your bridges somewhat.