It seems to me there are two ways you can go if you are involved in a relationship as illicit and taboo and incestuous as a relationship with your biologic sister. On one hand, shame can rear its ugly head, especially if the relationship is non-consensual and you've internalized secular or religious prohibitions. On the other hand, if the relationship is entirely consensual, with both sister and brother craving one-another, and societal prohibitions only playing a protective role--keeping the relationship entirely in a bubble populated only by the participant--well, then, the experience can be mind-blowingly erotic and ecstatic. The latter was the case with Sharon and myself, especially during our first five years, when we were in our 20's.
After making love at Sharon's place, we took a break for a couple of weeks. Work got in the way, as well as some real concerns. If we continued on with our thing, how do we juggle our relationship and real-life. How do we date? What do we tell one another about life (and sex) outside of the bubble? How long until the bubble bursts? I was the one who made the call this time. We agreed to meet at my place--this was getting serious.
We agreed--we needed ground rules. First, we recognized that we would always have a relationship--brother and sister--siblings. We agreed that we can't let our sexual involvement get in the way of real-life commitments. Sharon, at least, eventually wanted children, as well as a career.
Sharon said, "I'm in the exploratory phase of my life; what about you?"
I replied, "Basically, I want sex and money."
We promised to tell one another everything, every fantasy, who we might be sleeping with...nothing will be taboo, nothing to fear! How can you not be fearless if you're fucking your sibling? We also promised to keep this thing exclusively between us, unless we decide, mutually, that we want a multiple-partner sexual experience, though nobody involved but us need know that two of the participants are brother and sister. Plus, since both of us were and are into sleepy play and maybe other potentially dangerous games, we need to set limits so nobody gets seriously injured or even worse.