Things happened with my adopted sister (Part 1)

This story starts when an aunt adopts a girl, let's call her Agos, who supposedly had suffered abuse and mistreatment at home, something that one day my aunt comes to my house with my cousins and Agos (at my house we are just my parents and me, I'm the only child, my parents were over 50 years old and I was 23 at the time) my aunt starts telling us that Agos would fight with my cousins, so my mom says she can stay for a few days if it's more peaceful, plus Agos got along well with me, despite our age difference, so there wouldn't be a problem. At that moment my father wasn't home because of work (he was away from home for three months and then had three months off) so Agos would sleep with my mom. That day when my aunt and cousins left, Agos and I watched a movie together in bed, she lying on my chest while I hugged her, that's what we repeated every afternoon she stayed over, from my side being laid down embracing wasn't anything sexual, I saw her as the sister I never had at that time and for some months more. We played, talked, did everything together. I won't deny that despite being a girl and not being as developed in terms of breasts and butt, she was very pretty and her kindness made her even lovelier. Something that stayed with me for a month between my house and my aunt's until one day my aunt told my mom she was going to send Agos to an orphanage because she couldn't take it anymore, my mom tried to convince her not to do it but there was no use, as my mom got along well with Agos she said let her stay until my dad came back and then they would talk about adopting her. With the return of my dad we talked in the family and there wasn't much discussion since my mom and I were in agreement with adopting Agos, quickly we spoke to a lawyer to make the adoption papers and got a room for Agos alone. The cohabitation was normal until Agos had to go back to school, like me I had my car and I would take her and bring her back, since our schedules coincided for that and going to school. I always left her at the school gate and she would say goodbye with a kiss on the cheek, but when I waited outside, leaning against the car door, she would give me a hug and we'd leave. But one day when I went to pick her up, she came running and jumped over me and gave me a peck, I was surprised and only managed to grab her and make out with her, leaving my hands on her bum, I was surprised and didn't know what to do, she whispered in my ear let's go quickly and I'll tell you she got out of the car and entered, I didn't know what to do and stayed hard, when a group of three girls from the same age as Agos passed by, they were all very provocative with their shirts untied leaving their bellies bare and some tight pants, one of them said bye handsome and they laughed. As soon as she got in, Agos told me: sorry, but I did it for those girls who just passed I asked her why while starting the return trip. She told me that they were her friends, that one day they asked who I was and Agos said we were boyfriend and girlfriend, the girls didn't believe her and told her if they didn't see a kiss they would talk to me to find out if it was true, then Agos got cornered and thought of giving me a surprise kiss. I just laughed at her occurrences but she started crying, I had to stop the car to try to console her since she couldn't get home crying, I told her to calm down that it was our secret but not to do it again. When she calmed down we continued the trip and as there were only 20 minutes left until we got home, we kept talking, first about everyday things until she seemed relaxed like always and I asked her why she thought of saying we were boyfriend and girlfriend. Agos: because the girls were talking about their boyfriends and the dudes from 6th grade would talk, and well I didn't want to be less than them, and it's better to have a boyfriend older than me. She said this with a mischievous smile. Me: but you could've Said of your lie thus was I prepared Agos: and if you told me to do so? I: I don't know, it's already late, it's already done, but let it be the last time, I don't want to have problems because of your fault Agos: it's okay little brother, but can you do me another favor? I: another one? Agos: yes, because the girl are laughing at my clothes. This was said making a pucker like a spoiled child I: and what's wrong with your clothes? They look beautiful on you Agos: it's just that I'm the most covered up in the group and they annoy me by seeing me like a nun I: haha and what's wrong? I: come on, help me, please I: what? Like a slut? They'll never let you leave the house dressed like that Agos: come on, help me, these are my only friends, if I don't go out with them, no one will be my friend I: but it's impossible, I already know my parents, they'll never let you leave the house dressed like that Agos: oh wow, that's why I want you to help me I: how? You're not going to be able to leave the house dressed like a slut. Agos: it's not like a slut, it's in style. I already know how to do it, I just need you to let me change here in the car I: oh well, so you think being a prostitute is intelligent A: I was pretty bad at school I: let's hear your plan Agos: I'll leave the house dressed normally and change here in the car, it's not rocket science We were already arriving and we agreed to do that, which would be our secret. She throws herself on top of me and gives me a kiss on the cheek thanking my cooperation.