There are 2 assumptions in my mind!!!
we all can guess that sm ppl/terrorist fired all ppl in preet's mehandi/Haldi func, Ishaan's dialogue when preet said that she trust him " He can explain/prove her wrong, if she doubts him lyk asusual wife, but she s trusting him. but the truth is so big tat she wont be able to forgive him"
He isnt cheating her.. we can guess that, if he isnt cheating her, wat might be d truth which cld hurt her so much, if it isnt related to her??? since i can guess tat she had a painful moment in d past (i mean tat nightmare incident) i think he might be d reason/responsible for that moment in someway, which can hurt her badly as she s trusting him a lot now.
(d family was lived in pakistan at once) so Either he s a terrorist belongs to the gang whom fired all Preet's relations at her Haldi func, later he might changed due to his parent's dead/ his Bade papa, so he felt guilty and married preet w/o revealing anything N d Mystery girl might be also belong to d same terrorist gang, who s nw blackmailing him abt his past for money/something
Or Another way... since he is passionate abt country, why cant we consider lyk, he might be worked as a Spy or smthng and bcz of his mistake or smthng went wrong, the terrorist, whom he was spying might ended in firing all preet's relations.
i noticed in today's epi when trisha shouted at Ishaan that he joined d Hooda family jzt 4yrs before, so according to tat, his parents were died 4yrs before, after tat he s living with them.
his parents died 4yrs before, he married Preet 4yrs before and joined Hooda family 4yrs before. all this might hpnd jzt bcz of his 1 single mistake which might be d secret of his life nw.
P.S : sorry fa d long post!! 😆