My girlfriend went on a family trip for 4 days and I fucked her best friend. (BF-561)

My girlfriend's best friend, Hatsune Fumika, missed the last bus after drinking and came to stay at our house. Drunk, she took advantage of my girlfriend while she was asleep, and I couldn't resist... The next day, my girlfriend, completely unaware of what was happening, went on a four-day family trip, and we, knowing it was wrong, still went at it for four whole days...