My mother had a child with another guy before marrying my biological father. My half brother is 6 years elder than me. He has always been the distant handsome mysterious guy. I never really had a brother-like relationship with him because he preferred being alone and also because he was in boarding school so we didn't really grow up together.

So this happened one summer when we were at a family vacation. Our parents got drunk and disappeared from where we were. Bro came up to me and gave me tequila, saying "finally we get some freedom"
We drank in silence and then for the first time had a decent chat when the tequila hit. He got more beer, vodka, whiskey, we almost tried everything. We ran outside the hotel laughing and pranking people. It felt so good. We pranked one guy pretty badly and ran into the garden of the hotel. Tired of running, we dropped to the ground laughing when we heard some sounds. I got on four legs and and peeked from behind a hedge and saw my parents having sex like animals, completely naked. Shocked, I kept staring at them and bro came up beside me to see what was taking so long. We were silent and only the moaning could be heard along with the music that came from the party going on in the hotel.
I was wearing a tube top and short skirt and because I was so drunk, I didn't even realise when my tube top came down due to all the crawling. Suddenly I felt a hand on my breast which made me realise my top malfunctioned but I was too horny seeing our parents and didn't want bro to move his hands. I looked at him and realised he was out of it but I wanted him so bad. From the position we were in, I rolled and sat on top of him, rubbing my pussy on his crotch. He became hard in no time. I unzipped his pants and we fucked for sometime before he passed out. I was still feeling so horny I rode his dick as he lay there asleep. I heard a noise and I got up, adjusted my clothes and put his penis inside his pants and zipped it. I went to the tree to see if mom and dad were still there but they were gone. When I came back to where I was, the security was looking at my passed out brother and I told him I came here searching for him. After asking me a few questions he called a few more guards and they took him to his room. My parents were in their room, probably passed out, so they decided to speak to them in the morning.
Next morning, I went to check on brother and he seemed distant than ever. He didn't look at me the whole day. It was the last night of the vacation. Even during dinner he avoided me, even my parents noticed it. I felt embarrassed too, but I felt like I should apologize to him. So that night before bed, I knocked at his door. He opened the door and was shocked and embarrassed to see me, but invited me in anyway. I closed the door behind and immediately apologized for my behaviour last night. He came out of his distant state and in an extremely awkward tone told me that isn't as much as my fault as it was his as he initiated it. He looked so embarrassed like he was about to break down. I felt so sorry for him I blurted out that at least he did it because we both were drunk and engaging but I kept doing it even after he passed out. He was shocked and silent for a minute. He kept looking at me in awe.
Then after this frightening pause, he took my hand and lead me to his bed. He made me sit beside him and asked what do I mean. I couldn't answer but I blushed. Truth is, we never grew up together and somehow I really liked him. He held my face up and looked into my eyes and asked if I have any kind of feelings for him. I was so embarrassed and yet I knew the answer wasn't a NO. He read my expression and dived into a long kiss. We kissed and kissed like animals and then when we parted to take a breath he told me he always loved me and that he could never bring himself to accept me as his sister. This words made me go crazy and I jumped on him saying I didn't know how I felt but I did now and so we made out which eventually led to sex and it was awesome as fuck.
I know this is i****t but we never really grew up together and this is how we felt, there was no denying it. It has been one year since and we are going as good as ever. He is so much better than my past boyfriends, I wouldn't leave him for the world. We are so much in love but I'm afraid what will happen next. About our future. That is what scares me the most because the society will never accept us.