Why didn't you just secretly fuck her?
Girls that age love giving a boy his first time.
I fucked two of my older brother's girlfriends, and the one who is now his wife.
I would always look at them with puppy dog eyes. You just get in the habit of hugging them hello and goodbye when they visit your older brother. Then when they come over and he's not home yet, you make up some kind of deep problem you're facing, look sad, and ask for their advice.
Hug and touch as much as you can. Soon they will see you as a man in your own right. Hold hands, kiss, touch, let them touch your young body.
They will say over and over that you can never tell your brother. Agree, but realize that that gives you power.
Make sure you know beforehand how to finger and eat pussy. Your brother probably doesn't always give his GFs orgasms. Give them two each time, and take advantage of your quick ejaculation and rapid recovery, so you can fuck twice.
Don't pull out. They'll be upset but flatter them by saying they felt too good for you to pull out (true) and reassure them that the baby will look the same no matter which brother is the dad.
You basically want to be the adorable, forbidden, source of extra affection and sex.
My nephew is actually my son, but only my brother's wife and I know. She and I continued our sexual relationship as I grew up, as she got engaged to my brother, and after they got married. She says little bro dick just feels different. I'm hung bigger than him, so I always say back, Who are you calling little?
