Would you be talking about polyamory? There's a big difference between polyamory (loving and having relationships with multiple people, and reciprocating with your partners) and polygamy (marrying multiple people, most frequently only permitting men to marry multiple women, but not the other way around - commonly associated with Mormonism, but is actually limited to a few fundamentalist sects not associated with the main Church).

Is polyamory the new gay? I'm not sure what you mean by that. If you mean as in 'trendy', I hardly think that's the case. Being gay isn't trendy, it's just a part of who you are, and for many, the coming out process can be downright scary. Polyamory may have an aspect of trendiness right now, I'm not sure.

I'm poly myself, and have had both monogamous and polyamorous relationships. Poly relationships aren't easy. They take a lot of openness, honesty, and directness in your communication, with all your partners. Many people can't handle poly. But if you work hard at it, you can make it work.

One other thing; I strongly believe the principles behind polyamory that make it work (like being open about your feelings, asking for support or reassurance when needed) can be easily applied to monogamous relationships as well - a strong monogamous relationship ought to be like a strong polyamorous relationship, without the extra partner(s).