Your mom are having an affair. Your biological mom (Sakaki). You were already having an affair with Sakaki before your dad divorced her. Which was also the reason why she broke up with her dad wasn't enough for her anymore.
Somehow, you managed to wander into a lush and deep forest. You were going on a hike and next thing you knew, you were lost wandering through an unknown environment. Unfortunately, you met the wrong person at the wrong time.