How can it be? No way!
there are different kinds of cheating; emotional, physical....does your significant other know you are doing it? do you hide it from them? what are you talking about, sex, intimacy?? and if you aren't doing either now, do you want there to be?? <br />
if your answers to those are yes, then yes, I personally feel it would/could be considered emotional cheating.
Is the person only a friend or is there sexual or romantic interest? If the former, no. If the latter, yes.
Depends on what you sharing with that person and how much you really are enjoying each other's company so somehow it can turn into cheating without realising
It is rude.
Generally no, but the intentions must be considered.
depends on what you are doing and saying
Don't do it ! It can lead to feelings and trouble . This is how a person met the one they are currently with.
Would you rather be with that person more than with your partner?
Sounds like you want the best of both worlds