I would be careful if you live in the US in an 'employment at will' state. Your personal decision to be polyamorous can result in sanctions on the job, up to and including firing.
I don't say this to be alarmist-- when my relationship with a co-worker was discovered (we are both married, but are able to fraternize under our company's 'fraternization policy') we were both nearly fired because of the dissaproval of some key people in the office. The way it is, I lost any opportunity for a raise, and feel that my opportunities for growth at my office have all but disappeared.
It is unlikely that your personal choices will matter as much since you're not dating someone in your office. But, I would be cautious if you already feel vulnerable or unliked at your place of work. Being polyamorous is not protected under any laws, and employers can be unfair.