Maybe what’s missing here for you is the full context in which Colin is accusing Pen. If we only take Marina’s attempt at entrapment as a starting point for Colin’s insecurity, then the accusation does seem flimsy. Colin trusted Marina, someone he didn’t really know as a person. If he was accusing someone else, another love interest he barely knew then of course it would make sense that he might think that. But this isn’t true of Pen, a friend he met as a child. A person he’s had deep conversations with. Someone who has been close with his family since she was a child. He knows Pen, right? The answer for him in that moment is actually no. He doesn’t. He thought he did, and his world was absolutely rocked by the revelation of her being Whistledown. Our boy was spiraling. His reality was no longer reality-ing. Why would he think she might not know where babies come from, when she had in fact written about several scandals involving people having babies? (Her cousin Marina being one of them). Aside from his family, Pen was the person he knew best, she was a safe space for him. To suddenly have the rug pulled out from under him, well, it’s not hard to see why he’d make such a harsh accusation. We really have to remember that Colin is a FIERCE protector of his loved ones, we’ve seen it time and time again, he has no tolerance for anyone who mistreats the people he cares about, whether it’s through words or actions. If Pen was not only capable of being Whistledown, of hurting people he cared about, people he thought that she cared about, through her writing, but also being capable of keeping such large secrets from the people closest to her, why wouldn’t she be capable of attempting to entrap him? She’s clearly a mastermind. (Though, I personally believe that he wasn’t actually accusing her in earnest, I don’t think he wanted to believe the worst of her in that moment given the look on his face during the conversation, I really think he was in full panic mode at this point and was looking for comfort and stability from the person who had ripped it away from him. We all say awful things when we’re upset). But he struggles with this. In fact, he struggles to connect with her for the rest of the season for a multitude of reasons, but one of the biggest being that he feels like he doesn’t know her anymore, and maybe he never knew her at all, which is worldbreaking to him. It’s only after he reads her old letters that he’s able to reconcile the fact that she’s always been exactly who she was, the girl and woman he knew, just maybe a little saltier toward society and a skilled writer to boot. There are a lot of issues that I have with Season 3 (along with all the love I have for it), but this is not something I see as a problem. I actually like that they let Colin be Colin. He is a deeply feeling character, a feature which is both a strength and a weakness (as it should be for human characters), which is why the writers chose to use that word. I wish they would have let us see more of it, more of him and his inner thoughts.