We started "dating" you could say, when no one was around we would hold hands and kiss and everything teens dating do.
Then we started sneaking into each others rooms at night after everyone fell asleep to lay with each other and then it happened, we had sex. Every night possible I would go to her room or she would come to mine and we would have sex.
I kept my love hidden until she started dating a guy in high school.
For the next several months whenever our parents were gone we would look and touch each other. I began to get very attached to her and began to fall in love with my step sister.
Over the next few years it was agony for me because I knew I loved her more than a sister but was also aware that it was out of the norm.
Personally I don't think having sex with her is crazy.
We've tried anilingus before but only the once.
Occasionally we'll watch each other with our misters/mistresses.