I feel like I owe you guys a little more information outside of the physical differences.
My uncle on my mom's side visited recently and I caught two bits of conversation that reignited my suspicions. He was talking about how somone had behavioural problems because they're not blood related. I asked who they were talking about, but my mom quickly butted in to say it was about my cousin's daughter. It wasn't the words, but the uncomfortable look on both of their faces. I'm probably reading too much into this one.
I also overheard my mom tell him something to the effect of "your real kid is the one that visits". A lot of the meaning is lost in translation, but I took it as meaning that she sees me as her "real" son since her biological one has walked away from them and doesn't bother to call or visit, whereas I still visit from time to time. Maybe this is just some common saying. I don't want to read too much into this one either.
My dad once admitted to me that he unfairly punished me more often than my brother (older). It was a particularly unfair beating that triggered my first ever panic attack. It freaked him out enough that he actually addressed it. He told me that he didn't hit my brother much because he hit my brother in the head when he was little and he thought that was the reason my brother was so socially awkward. This sounded like a bullshit reason back then and it doesn't make any more sense decades later.
Maybe I'm just looking for an explanation for why my dad used to be such a dick to me, but he did provide for me and was financially there for me if I had any rough patches. He wasn't a complete POS. He was just unfair in how he spread out the punishment. I'd get the belt for "fighting" with my brother while he just got yelled at a little. My brother is twice my size. The "fights" were always one-sided, and definitely not in my favor. Also, my brother got it bad too, it was just way less often.
I don't like that I'm trying to justify my suspicions to a bunch of strangers, but it feels disrespectul to be in a room full of adoptees and pretend that I've gone through any of the things they have. I think I owe it to you guys to give you more information than just saying that they look different than me and we don't get along.
I'll probably delete this post and comments soon, but I do appreciate the time you guys took to respond to this post.