Hi zigzag,
You're polyamorous if you have loved or do love more than one person at the same time, or if you embrace the idea of doing so and identify as being open to loving more than one person at once.
Can be monogamous in practice, but embrace polyamory, polysexuality (sexual attraction to more than one, without the love), or whatever else.
Regarding the cuckoldry question... Well, yes and no! Traditionally, you might fall into the technical category of a cuck, though this usually refers to adultery - it's the idea that you are being duped, played, made subordinate by a woman. As others have said, this used to be (a very, very long time ago) a derogatory term, and it insinuated emasculation. The link with emasculation stems from the antiquated idea of men as superior to women - thus, if a woman was disobeying your ownership and control of her, (especially behind your back, which made you foolish), you appeared weak. Weakness was linked to femininity, and therefore you were seen as less masculine. These days, many people would argue that you're a bigger man for embracing your wife's love for another! Does it matter either way? Nah.
In terms of the fetish for cuckoldry (male form) /cuckqueaning (the female form), there are a few more layers. The emasculation can be there - in fact, this IS what makes it so erotic for many men. Typically, there might be: a man and his wife/partner; a 'bull' (hot masculine stud); and potentially a Domme (female dominant). Sometimes, the bull is a dominant male and no Domme is present. There are various configurations, but essentially, the cuck watches his wife have sex with the bull whilst being humiliated by others in the scene. The humiliation is largely based around the act itself ("The bull is better than you - you can't please me").
In the fetishistic sense, cuckoldry means that you are actually aroused by the thought/sight/sound of your spouse being sexual with another DUE TO feelings of emasculation/discomfort/insecurity/humiliation. In other words, you get off on the humiliation. If you simply like the visual of your wife with someone, that's more of a voyeuristic thing. If you aren't into, or dislike, the thought/sight of your spouse with someone else, you are neither a fetishistic cuck, nor are you a voyeur when it comes to her.
I think I just went on a fetish rant. Yay for cuckoldry. ~winks~