TIFU by giving my brother the sex talk

I posted here sometime last year about giving my brother the sex talk and I must say, it's not going so well. I'm typing this as I sit alone at my dad's place away from my mom's. My brother apparently thought that me being a good sister was free reign for him to think of me in an not so familial level. I look back to things I might have done wrong. I've always taken being a big sister seriously because again I have a lot of siblings and I live in a third world country in Asia where my parents have consistently pressured me to be the picture perfect daughter.

I never realized being a good older sister would have me end up this way.

So here's what happened. My brother got a girlfriend a few weeks right after my initial post. I thought all's well that ends well. at first he was secretive about it, until I found out the girl he got into a relationship with had the same name as me. If that wasn't weird enough, we both had glasses, too. I thought it was just a funny coincidence at first, my friends were the ones who pointed out a few other similarities but for me at that time, it just meant that my brother thought of me as a good older sister so he's modelling his ideal girl? I don't know why I was making excuses really.

Then they broke up and he had 2 nore girlfriends after. My friends kept pointing out other similarities I had with those girls, too, but again I didn't think much of it. Until yesterday. Another thing that happened in the past year was that my brother grew taller than me. He was slightly smaller than me before but now my forehead just sits right above his shoulder when we stand up. For family photos recently, he liked hugging me from behind and he kept asking me to rest my head on his shoulders.

It was my step dad's birthday yesterday and after a family photo, he kissed me on the top of my head. I felt cold for a moment, but he just smiled at me. I was beginning to feel nervous for some reason but I ignored it. After lunch time he offered to drive me aty dad's place as I live with my dad when I have f2f classes because it's nearer, and my PC is over there. Anyway, my brother stopped the car near a krispy Kreme and told me to order "his treat" he looked at me and smiled and that's when I started to feel genuinely scared. Because I saw the way he looked at me, and that's bno way to look at your sister. I never considered myself stupid or dense, but I didn't know it would go this far without me realizing. I know we didn't live together for the first decade of my life but we're half siblings. We came out of the same womb? Even if our father's are different and we have different surnames, I always thought it was fine and that I raised them to think of me as their big sister.

Now everything is flashing to me. All those times he told me that my step dad's last name would fit better with my first names as it starts with the same letter. Or all those videos he sent me of siblings and dating and him as long me if ever we got on those videos what people would think. Even all those times he kept intimidating my exes, we all thought he was being a cute brother for gods sake! I feel like a failure as a sister and a child. I feel guilty like I've led this to happen when I know logically that I didn't.

He's been texting me innocently, asking me what I'm doing, but I'm now so scared to respond. I feel like anything I do will make this blow out of proportion. I don't want to tell our mom, or either of our dad's. I get along great with my step dad and I don't want to even think about what he'll think considering he's a policeman. I've never felt this stupid

TL;DR: I realized my brother may not Iike me as a sister at all and I'm feeling lost.

Edit: Thanks for everyone who's commented so far. It's only been a few hours but I've received such thoughtful advice. For context my brother's about to turn 18 and I'm 23. The most he's crossed the line with his questions were asking me to put a condom on him as a demonstration and asking me how to properly eat out female genitals. The first I showed him with an eggplant, the second I had to ask him to google it. Also, as mentioned in my first post, the porn he was watching on my laptop were about step siblings. We're HALF siblings so I didn't really think about it too much.

I will speak with him this weekend once I gather my thoughts. Thank you for listening.