Secretly fucking your best friend while her husband is around

After not seeing each other for a long time, a group of four close friends go to the hot springs. And this trip's purpose is adultery, a married couple secretly has sex with each other and this is the best opportunity for them to be together a lot. Covering the eyes of those around them, after getting drunk they found each other in the bathroom and had sex all night long. Some time later, this girlfriend became pregnant and her husband was likely to blame her.