Should i say yes??????

This is a continuation of my last question, about whether he was too old. Okay well my friends older brother,whos 16, likes me,im 14, and i really like him too. And he asked me out but i thought i should ask my friend if it would be okay if i started dating her brother and she said she wasnt really comfortable with it. Now heres where the problem comes in, I reallly really really wanna go out with him but i dont wanna put my friendship in jeopardy. But i have liked him for a while, tho i never told her that. So should i try and reason with her? or date him in secret? or just forget it or something? please help!