Big Sister Was My Instructor

My sister is two years older and could be a model. She always been into fitness and a vegan.
When we were in high school, my friends always made comments about her. She's 5' 2", brown hair & eyes, tan, tone body and tan. I'll admit checking out her sports bra & panties in the laundry.
My sister and I have always been close. She had a boyfriend at the time and when our parents were away at work, she'd have him over after school so they could f*ck in her room. I promised to be quiet and she'd do my chores and drive me places.
I was 15 and summer had just began. Our parents had been saving up for this moment and went to Europe for 3 weeks with friends.
My sister was open with me on how she planned to have fun with her boyfriend David while our parents were away. A few days before our parents left, they broke up because he was cheating.
My sister's normal routine was to go for a run in the morning and shower after.
I was in my room gaming and she came in wearing a towel and asked to talk and if I could help her out. She likes to talk so I shut everything down.
She was blunt and told me she was horny and other methods were not working. I was naive so she explained what that meant. She also knew I was a virgin from previous conversations. That's when she suggested we have sex. I almost came in my shorts from excitement. My only concern was what if something happens like she get pregnant. I'll never forget her saying, "Oh, it's OK. I'm on birth control but you're also going to wear one of these." She showed me a condom and said, 'It was intended for David but he f*cked that up. Now, you can use it.' That opened the flood gates and we did it all the time. I'll never forget the first time we did it without a condom. She was on birth control but also assured me the timing was right for her cycle, it was a couple of days before her period. Thankfully, she did start when she predicted.
That was the best summer!