I think you can word it however works best for you, but it's a very well established and used term both in societal and therapeutic circles.

Trust can be broken at many different levels, trust can be broken in a way that's hurtful and infuriating without causing emotional distress. Certainly betrayal by a friend, family member or business partner is an awful experience but in most cases these do not have the hallmark of the unfaithful person having developed a new bond that mimics the basis of the relationship. Emotional infidelity usually involves the perpetrator buildingvs second connection that has many of the signs and feelings of a genuine full relationship, which directly undermines the relationship they're supposedly already invested in.

1. people that screw over their business partner do so for financial gain, it's less intimate and business often comes with such risks. A business partner can do other deals without it having any significance to your business arrangement.

2. The expectations are usually vastly different of friends and family members than of a partner, certainly when it is a marriage. One can easily understand & accept that they don't know about new people their family members get involved with. If your husband were to start having regular lunches or after works drinks alone with a new friend or colleague, that might be something you'd expect to be kept in the loop about. Trust in relationships is commonly built by, amongst other things, revealing ones life to the partner, introducing them to people that are of significance. If eg your sister starts dating a new guy you likely have no cause to be upset that you haven't been told about this new person, and the relationship didn't threshed to replace your own - quite different if it's your spouse. The very act of sharing information about relevant others in your world solidifies bonds already established & increases feelings of trust and safety. When it has to be covered up and hidden then it's likely not a mere platonic friendship, a violation of trust odd taking place even though it's not yet a sexual infidelity

3. People tend to invest a great deal more of their emotional energy and sense of safety in their romantic partnerships. This generally increases with age when relationships become more serious and begin involving children, joint finances etc. A betrayal of that, leaves people's worlds split asunder. By virtue of the very nature of long term committed sexual relationships that bond is very close, very intimate and closeness brings vulnerability. People share their past, their hopes and fears and pains with each other. People usually trust their partner with a level of vulnerability that simply doesn't equal that in business. Having some money stolen is argued but not comparable to heartbreak and having to see the face of that person every morning or going through dividing assets.

I think time is also a factor, I'm not taking about a one off lunch, an ill thought out emoji or a slightly flirtatious singular response, I'm talking about a partner engaging with another person at the level that would only be expected to occur between a couple. I'm talking about consistent deception by the person you love and share your life with, I think for most people in love the experiences is generally devastating and it's always at an emotional level.