When done correctly, no it is not cheating. Polyamory essentially means being in multiple relationships at the same time where everyone involved knows that there are multiple people involved. So you can have multiple boyfriends or girlfriends and each one knows that you have multiple boyfriends or girlfriends and typically they also have multiple boyfriends or girlfriends who you know about. No trust is broken and no one feels betrayed because all cards are put out on the table and everyone is okay with it. If someone isn't okay with this set up, they need to either get out or talk to everyone who's involved. It can be seen as non-exclusive committed relationships.
On the other hand, cheating is usually done in monogamous relationships and is secretive where you are doing things behind your partner's back. It is considered betrayal because you have previously committed to be exclusive and you have broken that.
Honesty and openness are what distinguishes polyamory with cheating. They aren't the same thing nor does one make you the other. The intent of what you're going through and the communication involved is very important in determining between the two.
