Frustration sets in after enjoying the afterglow. This damn circle still works even outside the blasted ritual. And how much more energy can it possibly absorb before being completely filled up. perhaps it was time to try and call in a specialist upon whatever magic this was. It seemed like it was based on an incubus to be truthful so maybe summoning a sex demon might give him the insight needed to control it. However that is rather dangerous and extreme for the first idea so maybe there was something he could divine from elsewhere. Still he would have to carry them into more comfortable quarters and of course the youngest sister as well. She would also need to be tamed and deflowered eventually. But it seems that so long as he doesn't fill them up with his seed, he can avoid the issues.