How to save my BF from a vixen?

Hi, I am a 30 Yr + normal person living in HK. I have a steady BF. We got along fine but he is more adventerous in bed than I am. Recently he stopped taking any interested in me. I found that he is seeing a fillipina in his office. She is 20 yrs old. I confronted her. She said that she is married, her husband works in Saudi Arabia, and she is only trying to supplement her income. She will leave my BF the day she finds a richer man. Meanwhile, she is giving my man everything he has wanted in bed but I am not willing to provide. BJs, coming in mouth, handcuff. They even videotape their sessions!!! I am concerned about my BF. I can forgive him if he forgets this **** immediately and emerges clean from a medical checkup. But I don't think I can ever match this girl in her actions. My man is a good one at heart and I can tolerate his mistake. But how to ensure that I can retain him for good? Anyone with similar experience?