Cheating is in the eye of the beholder!
Naturally if one is having sex with someone else outside of their relationship most people would consider it cheating. However once you go beyond the "obvious" everyone has differing opinions about what constitutes cheating.
Some people believe "emotional cheating" is a betrayal of their relationship. Having secret or known friends of the opposite sex, meeting them for lunch/dinner/movies, and other activities are viewed by them as time you should be spending with your mate.
The mistake a lot of couples make is they insist upon trying to "change" the other person's way of thinking or demanding they accept it knowing he/she is unhappy about it.
This is not a matter of one person being "right" and the other being "wrong". What it comes down to is "agree" and "disagree".
Couples who naturally agree on the major things in life tend to be happier than those who don't.
Instead of expecting someone to "change" you'd be better off finding someone that has no problem with their mate having friends of the opposite sex. It's better than being dishonest and sneaking around.
There are only two ways to experience joy and peace of mind in relationships: We either get what we want or we learn to be happy with what we have. The choice is up to us!