IS AN AFFAIR A FORM OF EMOTIONAL ABUSE?
First things first...the term 'abuse' has been used more and more, in the recent past, to the point that just about anything can, and has been, called abuse. What we used to consider relatively normal behavior, such as yelling at someone when angry, or cursing at someone, or calling someone a name, now is considered emotional abuse, or verbal abuse. Losing your temper around someone is now considered a form of emotional abuse. Speaking in sexual ways, or commenting on someone's physique, can be considered a form of sexual abuse. Failing to pay sufficient attention to your child is now considered a form of psychological abuse. Manipulating someone into doing something, such as using a guilt trip, or cutting them down so that they want to do better, is now called psychological abuse. So, I think it would be safe to say that we've gone a little crazy, overall, in terms of what we are calling 'abuse.'
That being said, the question as to whether or not an affair is a form of emotional or psychological abuse certainly deserves a fair shake.
When considering whether an affair is a form of emotional or psychological abuse, one could simply look at the end result. Does it cause psychological, emotional, or physical harm? If the answer is yes, then one could define an affair as a form of abuse. However, doesn't abuse have to be intentional in order to be considered abuse? Well, actually, no...if we only called it abuse if it was intentional, then when someone has an emotional meltdown and starts screaming, and hitting, but they really did not mean to hurt anyone, they could make the same claim. So, no, it does not have to be intended to harm...the end result just needs to be that there was harm.
Of course, you may disagree. If you have ever had an affair, it may be very disturbing to be told that you were emotionally or psychologically abusing your partner. And you could always disagree with this conceptualization. Your choice. And, one could argue that the whole societal movement to expand the definition of abuse to include many new things is absurd, or excessive. This may be a valid argument, but probably not of much use at this point, because it does appear to be a strong movement that is propelling the expansion of the definition of abuse, and this movement does not appear to be losing steam.
Can an affair be a way of intentionally causing emotional or psychological harm to a partner? Absolutely. Sometimes, affairs are a way of retaliating; what we term 'passive-aggressive.' If the one having the affair feels as if they have been mistreated, or abused, by their partner, they may have an affair as a way of evening the score, so to speak, or as a way of re-asserting their 'power' in the relationship. In that scenario, they are not necessarily attempting to end the relationship, but rather to 'get even.' Still, if the result is emotional/psychological harm, then yes, it is abuse.
In some instances, when someone has an affair, they are aware that this will potentially harm their partner, if their partner finds out, and they may actually be very careless in terms of trying to hide the affair, because they may hope, on some semi-conscious level, that their partner WILL find out about it, and WILL feel abused, so that they will end the relationship, which is what the person having the affair was hoping for. In other words, they use the affair as a tool, in part, to destroy the relationship, because they were ready for the relationship to end but did not want to take the responsibility for ending it. This is a method that people use when they are very uncomfortable seeing themselves as a mean person; ending a relationship, in their view, is mean, but 'falling in love' with someone else, while in another relationship, is merely happenstance and not at all their 'fault;' it is just fate. So, in their view, they are not mean, but rather, simply being swept away by fate. Much easier to digest, for them, although it does not change how the other person feels, and does not make the harm any easier to digest, for them.
Can an affair sometimes not be abuse? That is a more difficult question. If an affair occurred, but it did not cause any emotional/psychological harm, then one could argue that it was not abuse. And, if the affair was 'approved' by the partner, perhaps it is not abuse. However, this is a slippery slope, because even 'open marriages' or 'open' relationships can cause emotional/psychological harm, even if both were consenting, in the beginning...sometimes (maybe oftentimes) the open relationship benefits one partner more than the other, or the other partner does not feel the way they thought they would feel, and it becomes an emotionally harmful situation. So, just because there was consent, prior to the act, does not mean it is not potentially emotionally or psychologically abusive.
In general, it does seem that there is a fair amount of support for considering an affair a form of mental abuse. And, if the impact on the partner is taken into consideration, when determining how serious a form of abuse it is, then in many instances, affairs may be one of the more serious forms of abuse. And, interestingly, affairs are one of the forms of abuse that no-one seems to call abuse, and which seems to fly under the radar as nothing more than one of the risks of 'love.' Interesting.