I strongly disagree and think this is a black and white way of thinking. One of my best friends that I've known over 12 years and I had a weird phase where we would get really drunk and hook up periodically for a year or so. There were definitely some emotions involved, but we ultimately concluded that a relationship would not work between us and stopped having sex. We remained close even after this.

I have now been with my current partner for 6 years and he has been with his for almost 2 years. We are still best friends with zero sexual tension. My partner knows we used to have sex and trusts me enough to know I won't cheat on him. Life is complicated. Friendships are complicated. I have never cheated and have no desire to.