Some FAQ-answerable questions

This girl that I've been friends with for years asked me to do a threesome with her and her boyfriend, who I've come to like as well (not sure how much I feel for him yet). I went through with it and it went really well. I hear polyamorous relationships are like equal love triangles where each two love each other. I kinda want to bring up the topic with them. But I'm afraid that I'm just lusting after her boyfriend since I don't know him as well. Can polyamory be one girl just having 2 loves?

Yes, that is called V-shaped polyamory. In this case, the girl you're talking about would be the center point, or "hinge," of the V, and you and her boyfriend would be the other points. You're both romantically connected to her, but not to each other. There are lots of ways to be polyamorous and practice polyamory - check out my resources here.

So, how does polyamory work? I know it’s a relation with more than two people, but after that I don’t quite understand. Do the three or more people all love each other romantically (and possibly love each other equally) or is it where one or the other first two people each date separate people (those separate people don’t live the other of the first two)? Or, could it be both ways?

Both arrangements that you're describing fall under the umbrella of polyamory. To learn more about the first style that you described, try searching for the terms "closed," "triad," or "polyfidelity" in the context of polyamory. For the second, try searching for the terms "hinge," "V-shaped polyamory," or "polycule" in the context of polyamory. Check out my resources here.