Just found out

I’m 41 and just found out the other day I was adopted. Last Thursday (thanksgiving) I had a little too much to drink and had an emotional conversation with one of my cousins. I told him that ever since I was a kid, I would see my mom and sister lie to people all the time, and I couldn’t trust them or anyone because if they could lie so easily and so often to others,what are they lying to me about? I told him I have always felt like there has been something that happened to me when I was younger but I don’t know what. That night he left and he didn’t say anything. He came back to my house that next Tuesday to talk and told me if I have any questions about our family, that I can ask and he will tell me the truth. After some talking, it somehow came up and I asked him if me or my sister were adopted, and he told me that I was. Also my whole family has known this whole time too. After my moms first son passed away, they thought she couldn’t get pregnant, so they adopted me, and very shortly after discovered she was 3 months pregnant with my sister. They went so far into the lying as to even change my sisters birthday so I would think we were 10 months apart in age, when Infact we are only 6 months apart. My cousin said that him an another one of my cousins, wanted to tell me so many times throughout my life, he said they were really close to telling me at some point 6 years ago, but my sister was dead set against it. My cousin said when I opened up to him on thanksgiving he felt really guilty and had been fighting with himself on if he should tell me, he even went to the family shrink for his opinion, and that’s the day he came to me and told me. I was completely shocked, I feel like my whole life was a lie. I know I’m lucky that I got adopted into a great family but I don’t understand why it had to be kept from me for so long and why my sister was so dead set against anyone telling me. I still can’t believe they even went as far as to change her birthday so I wouldn’t find out. And when someone (I’m assuming my mom) told my sister, why didn’t she tell me then as well? I haven’t spoken to my sister about it yet, I think I’m still a little angry, and it’s still new and raw. My mom has dementia and I don’t want to ask her now cause I don’t want to cause her stress and with her condition being so bad I just don’t think it would be a good idea. So I’ll have to give myself a couple days and ask my sister but I don’t even know where to start. In the meantime, I ordered a kit from ancestry.com, maybe I can find out some information through that. Well that’s my story for now...