Basically, I think he's acting out of character because he's in love too. Its not just any diary, but that of a woman he loves. I know, you guys have been calling Purab a saint and a devta, but even saints and devtas have limits. Purab is but a human.
I dont know what he intends to do with Gulmohar. But, I doubt it that he will destroy it as the company is very close to Jassi's heart. All he wants to do is to make Jassi realize Armaan's manipulations.
Anyway, I'm going to see what he does after reading the diary.