Me 18 (f) and my best friend 18(f) have always been like sisters i used to live in their house and we done everything together. Until we Went on holiday and had a big fall out and we didn’t talk for about 3 months. Her and her brother (24) have always had a very close relationship and while i was friends with her me and him gained a very close relationship. I have always found my friends brother attractive and it has been something i have been very open about and I have always made jokes about it throughout the whole family. So we made up in the past 2 months and have gotten a lot close meaning I have been spending more time at her house where her brother still lives. He started talking to me on snap chat then things gradually started Getting closer and he started talking to me every day. He likes to go drives and smoke devils lettuce so one day he asked if i wanted to go a drive with him and one thing led to another and we ended up kissing and other things of a sexual context. This happened a few more times and one day when i was staying at my friends and he asked me to go out the back door to smoke with him while she was sleeping this is not an uncommon thing considering how close we are. We ended up spending 5 hours with each other and doing other things of a sexual context in the garage. I have recently moved into my own flat with my other best friend (19 ) M and her brother has been coming over in secret. She is completely unaware of any of it but i feel like it is getting more serious and its killing me not telling my best friend about a boy i like but im so scared she will fall out with me if she finds out im really stuck on what to do. She is having a party at her house on Friday and her and her brother invited me and i am scared if im drunk i will let the secret out so do i just tell her or do i wait what do u all think lmk in comments.