Microcheating is the term for small things you do that could have whispers of infidelity, without even being physically unfaithful but just as dangerous.

Signs of micro-cheating  (Bustle)
Microcheating is the term for small things you do that could have whispers of infidelity, without even being physically unfaithful, and can take you into territories you might regret. Think of it as the little sister to emotional cheating. We explain exactly what micro cheating is and whether or not you are guilty.
“Microcheating happens when you create small opportunities for affectionate behaviours that fall outside your relationship,” explains sex and relationship therapist Tammy Nelson, PhD, author of The New Monogamy: ­Redefining Your Relationship After Infidelity. You may be doing it when your partner is not around or even in front of them and with or without their knowledge. But given that such a habit can build up to something more, it can spell trouble.

What are common signs of micro-cheating?
Although physical cheating is quite easy to define, microcheating tends to be more of a grey area. However, common examples of this type of infidelity can include:

Lying about your relationship status
Obsessively checking another person's social media feed
Texting or contacting someone without your partner's knowledge . . . and trying to mask the evidence
Listing a so-called "friend" under a code name in your phone
Engaging with a past lover, whether it be in person or on social media
Sharing secrets with someone you're attracted to outside your relationship

Microcheating whilst in a relationship.  (The Independent)
How to be sure that you're microcheating
If you're not sure whether your own behaviour counts as micro-cheating, certified coach Jillian Turecki suggests asking yourself this: Would you be acting the same way if your partner was sitting right next to you? "Anything that’s done on the sly or is not congruent with who you are in front of your person is a problem," explains Turecki.

No matter how small the act of microcheating feels, Turecki suggests thinking about what you value. "Instead of thinking, 'I can’t micro cheat,' it’s more useful to think of what you value. If you value integrity, respect, and loyalty, then commit to acting in accordance with that. I believe that is an important standard everyone must have for themselves, coupled or not. It leads to greater happiness as well. We like acting in alignment with what we value. It feels good."

Does this mean the end?
But should this behaviour really be a deal-breaker in a relationship? If it makes you feel uncomfortable or insecure in your relationship, then perhaps.

However, it's important to talk to your partner about the issue in a diplomatic and rational way, taking are to explain the observations you have made, and how they have affected you. 

If you think "there may be more to the story'' it may be wise to talk to your partner about the situation and ask calmly "Is there something I need to know about your feelings for this person?"

Another effective approach would be to ask: "How would you feel if I did something like this?". Sometimes people do not understand the magnitude of their actions until they are the ones on the receiving end of such behaviour. A little empathy can go a long way.

Microcheating is largely forgivable but the danger is that it can lead to cheating in the more traditional sense. Sometimes, little actions have subconscious effects on us and before we know it, a small fancy can spell big trouble for your relationship. Always bear in mind what you have and remind yourself about why it's not worth it to put what you and your partner have built at risk.

Nice.

A nice piece. I guilty of it. As I'm typing this, I'm also waiting for a reply from my married ex. Cos I replied a message from her which also required an answer. I did dat just before typing this comment.

I think majority is guilty.

Well, I was once guilty... I will try as much not to do it in my next relationship which I hope will lead to marriage. In other words... I need a girlfriend

I guess 99.9% of us are guilty.

guilty till the day I pass away.