though i don't know the whole story - my bet is that NO - you were not to blame. she was the adult - and a parent at that - and responsible to keep you safe. you were a kid - legally a child - and not expected to be the one setting the tone for the relationship. 15-year-olds may be physically "mature" but are definitely NOT emotionally or mentally mature. even if you think you could have stopped it, the power balance was not on your side. authority figures weild much more power than kids.
IT WAS NOT YOUR FAULT!
As my life goes on I believe somehow something's changed
Something deep inside...
I've been searchin so long to find an answer
Now I know my life has meaning
Now I see myself as I am, feeling very free...
When my tears have come to an end I will understand
What I left behind: a part of me. Chicago