Totally agree with you and i am so glad that there is someone who is thinking just like me that ranbir still dont believe that r is changed but he is not showing it outside.
Now i can conclude that the main reason why ranbir is not present in the last few episodes is becoz he wud have immediately figured out that r did it and that she is still the same not changed at all if he was present during last few episodes.
I am not at all surprised that he dont believe r changed. After what all he suffered due to r he will never be able to trust her i felt that during his initial talks about r after the leap. prachi will be shown dumb and ranbir will be smart.