Happy 3rd anniversary to all fans of the show!
The peḍhā revelation may have been delayed due to whatever caused Narapat to disappear from the screen shortly after sūramārī. However, I think it was better for drama that it stayed in the background with Mangal refusing to let it go, until the couple had love and intimacy and parenthood to lose if Shiva stopped trusting Siddhi. If Shiva had forgiven Siddhi for drugging him (the way she forgave him for drugging her to kidnap her), and then fallen in love, it would have been sweet, but considering how much Siddhi had to accept about Shiva - who didn't change his ways for her, and her overall disadvantage against his household, his gang, his partisan morals, his physical strength, and his temper, I found it satisfying that Shiva was vulnerable to Siddhi too.
Siddhi had helped Narapat to expose Ātyābāī's papers and intercept the sāḍyā that she wanted to give voters. Siddhi had watched Shiva beating and pillorying other people for those incidents, and she never confessed. Of course, Siddhi felt more guilty about the peḍhā, but I understood Malini's advice and Siddhi's choice to keep quiet about everything, knowing how awful Shiva's vengeance could be.
In contrast, Shiva wasn't afraid of Siddhi. When Shiva teased Siddhi for taking so long to feed him at sūramārī, asking if the peḍhā wasn't poisoned, it was obvious that he expected no trouble from her after beating her brother the day before. So, whatever secrets Shiva kept from Siddhi (e.g. his regular visits to Saumya, or whomever he was beating each day) were not written for suspense. Whenever Siddhi found out that Shiva had interfered in her life without telling her (intimidating Saguna to give up land to Sagar, which got Nandakumar arrested ... hall ticket ... cancelled exam), or whenever Shiva openly attacked something or someone that Siddhi loved, it was never a serious possibility that the marriage would end. Siddhi tried to leave occasionally, but the story required her to come back. We viewers may have felt that Siddhi's secrets were more of an obstacle to the couple's happiness than Shiva's ongoing misdeeds that were out in the open, because storytelling dwells on secrets and moves on from violence, but realism might be the opposite.
I imagine that Shiva didn't forget Siddhi's hesitation to feed him the peḍhā; he suspected that she knew it was drugged, but he chose to be grateful and trust her.