The key to determining whether behavior can legitimately be classified as an affair is whether or not there's SECRECY regarding the outside involvement. Since secrecy is a critical component of a strong emotional relationship with someone other than your partner, it IS (even without involving "sex") still an affair.

It's been clear to me for many years that it's the "deception" (whether sexual or emotional) that creates the most long-term damage to the trust and the future of the marriage. As I've repeatedly stated, most people recover from the fact that their partner had sex with someone else before they recover from the fact that they were deceived. An affair, in the final analysis, is more about "breaking trust" than about "having sex."

Here are the responses to the following question in an online poll we took on the site a couple of years ago:

"If your partner has had an affair, what was the most difficult to overcome?"

Women's responses:
That they had sex with someone else - 28%
That they deceived me - 72%

Men's responses:
That they had sex with someone else - 30%
That they deceived me - 70%

Emotional affairs are growing and affecting a large number of people, primarily due to more workplace connections and more online connections. Since this is such a significant issue for so many people, I'm posting some information below from one of the Questions I recently responses to on the site—and making it a permanent part of the Articles about Affairs on the website.

What makes it an emotional affair?

It's an emotional affair if…
--I'm keeping the details of my relationship secret from my spouse
--I'm saying and doing things with the other person I wouldn't do with my spouse present
--I'm sharing things with the other person that I don't share with my spouse
--I'm making an effort to arrange to spend time with the other person

Most people who get involved in an "emotional affair..."
--weren't looking for an affair
--didn't INTEND to have an affair
--didn't think they were vulnerable to an affair

Emotional affairs either end or they escalate.

It really doesn't matter whether someone thinks an emotional relationship is totally harmless. The fact is that in most instances emotional affairs are just affairs that have not YET become sexual. They either end or they escalate. So (as with any type affair), it's critical that all one-on-one contact with the third party be severed—before it escalates.

The results of my survey of people who had online affairs indicated:
--79% were NOT seeking an affair
--49% eventually developed into a physical sexual relationship

If there is ongoing interaction with someone with whom you have been very honest in sharing your deepest thoughts and feelings, this can generate a feeling of closeness that stimulates even more sharing—and more closeness, and on and on. Eventually, this relationship can become extremely close and an emotional attachment develops, causing serious damage to the marriage—whether or not it ever becomes "sexual."

For more on this issue, see:
Article in Psychology Today Love, But Don't Touch
Article in Marie Claire The dangerous new infidelity you need to know about
Article in Ladies Homes Journal about Emotional Affairs
Article in USA Today about Emotional Intimacy