Personally I think everyone has their own tolerance levels, but I also believe there is a bullshit double standard applied to this subject.
If a guy screws 100 women he is a "stud", but let a woman do it and she is "whore" or "slut".
I disagree that "Promiscuity and infidelity go hand in hand" as an absolute. Both of my marriages and most of my LTRs were with women that had played the field like myself. Libidos that are compatible usually help a relationship. People just don't wake up being good at anything, it's called experience.
The breaking point with all of my relationships usually involved external forces (money, assignments, work, relatives, etc).
I will also say I have seen a lot of "high school" sweetheart and "virgins" marriages go to shit in a much more ugly way than the typical "promiscuous couples" that usually just part ways.
Obviously having said all this "protection" is a must. If your going to paint on a lot of canvas, you better take care of the brush.