Let's say you had a man who provided for you, lavished you with expensive gifts, gave all his love and attention to you, was attentive towards all your emotional needs etc but decided to cheated on you with another woman that was purely a physical encounter (no emotional attachment involved)?

Would that still be a huge deal in your book, would you be able to excuse it or forgive it? As long as the very security or access to his resources isn't threatened.

From an "evolutionary" point of view, men feel strongly about getting cheated since he would feel like a "cuck" in the situation (providing resources just so that a superior man would reap his rewards) and have his genetic legacy threatened via paternity fraud. However, it wouldn't make as much sense for woman to feel the same way as long as she has her needs met for attention, emotional support, security and resources (provided there was absolutely no chance of the man leaving her for another woman).