Personally I believe if you look at it as in “falling” into temptation then there will always be a problem.
In many marriages there will be happy times and struggle times. Though most couple not to the degree you are taking about (eg: physical or psychological abuse) but in every relationship there will usually be occasional arguments at some point.
Looking at it the way you look at it, can’t there then become potential to be unfaithful anytime there is difficulty?
What if more serious difficulty happens, (for example if the husband or wife becomes disabled)? This can cause stress, loneliness etc… Will the other person then resort to cheat?
No person is ever really totally innocent in a marriage (even if they feel this). Many people though dislike infidelity (including non faith people I know) for what it causes, and resolve to not be unfaithful in any circumstance.
Sexual infidelity is important because it is the traditional understanding of infidelity & what Jesus refers to when mentioned adultery.
Before there was American words like “emotional infidelity” etc, adultery was understood across many cultures and eras the same as physical cheating & as a deception/betrayal/secret.
It’s not just sex, many people can consider kissing another man/woman as degree of of cheating. Feelings come along too.
different types of unfaithfulness.
Sorry but I’m not really sure what the different other types that you mention look like?
I don’t think things like workaholism, emotional neglect, poor communication etc are unfaithfulness although they definitely can be immaturity etc.
I see it as American type psychologists just complicating matters trying to create new definitions of infidelity etc…
In most other cultures, it’s understood for what it is without words long before “so called experts” starting defining it.
Even if emotional infidelity exist for somebody and is real, isn’t it very possible it will eventually become physical anyway?