[Advice Needed] My Boyfriend Had s*x With His Cousin! I Am Confused, Please Help!

images (13)My boyfriend got a job in Owerri and he had to stay with a his uncle who resides in the city. The accommodation was meant to be temporary but along the line, his uncle told him he could stay for as long as he wanted as his family are usually not around. He said his presence would give life to the house so it wont make the place dormant. He decided to stay there. While staying there, a lady, a distant cousin to his uncle’s wife started her masters in FUTO. Since she was a masters student and didn’t want to spend much on accommodation, his uncle told her she could stay with him in the house.
They started well but along the line he always complains that she opens the door to her room while dressing up. He also complains that she wears skimpy dresses around the house. Trouble started when my boyfriend told me she came to his room with just a towel and started touching and caressing him. He was able to gather his emotions and he told her to leave his room. The lady came again but this time, He confessed that he could not hold him self and he did everything foreplay other than the s*x itself. I started getting bothered and i told him to stay away from her and warned him to always close his door. Just last Saturday, they were both home and while in the living room, he said she came on him again and did all sort and this time, they actually had s*x. He said he could not resist the temptation and it was as though he was not himself. When he told me, i just started crying. Sincerely im tired of the relationship. I have been thinking a lot about the issue. Its as though i cant trust him again. I don’t even know why he tells me all. Should i call it quit? Or should i move in with him in Owerri? I am confused. Please help!