WHAT DO YOU CONSIDER CHEATING?

I am not an expert, but from what I have observed – I have concluded that this question means different things to different people. Most people in traditional monogamous relationships believe sexual infidelity is cheating, but do you believe it's deeper than just that?

What if you're in a relationship and find yourself connecting with another person? I've heard people saying that you can't get all things from one person. Different people bring out different qualities of your personality. But when you are in a committed relationship, should you give up these connections with other people? 

Is it cheating if you have a mental connection with someone and pursue a relationship with them? Could this be the definition of Friendship or is this an aspect of Cheating?

I have a friend who doesn't realise she is in an intimate relationship with a married man. Don't misunderstand me - they do not have a physical relationship. In fact, their interaction consists of only phone calls.

But he shares his fears, dreams and frustrations with her, the things you would expect him to share with his wife. I've witnessed them talk for an hour with ease. He reaches out to her when he feels defeated, sad or even excited. He calls her every night to talk about his day. Her voice is the last thing he hears before he goes to sleep.

Their conversations are platonic of nature, no sexual chit-chat. I believe my friend fills a void in this man's life and he fills one in her life. She refers to him as a friend, but would his wife have the same understanding? Are they just really good friends or are the lines of friendship blurred? Do you considered this cheating? Where do we draw the line?