I read online that the famous story of Qasim ibn Al Hassan in Muharram is fabricated. That story being that he was martyred when he was newly wed or was going to get married. My hussaynia always includes that part of the story during Muharram. Is it true that it’s not apart of the story and history of Karbala? If so, why are knowledgeable sheikhs still discussing it?

Not that it’s fabricated but we don’t have any hadith evidence of it. Some researchers have said there are some clues that he was going to marry Imam Hussain’s (a) daughter, but there is no evidence that it happened. Poets usually mention this wedding symbolically, not literally—meaning they grieve for him not living to have a wedding.