She's fallen in love after two fucks? I have a feeling it's just lust; there are lots of brain chemicals at play
. Maybe asking for some time until she gets together with him again will let some of those feelings settle down. I also think the two of you should really figure out how you want poly to be expressed in your lives. Seeking out separate love interests or trying to make it work with other couples? Do you really want poly or do you want to just "play?"
The thing is, maybe you needed more time to get to know both people in that couple before getting jiggy with them. You might have found something that would attract you to the wife if you had developed some sort of friendship/relationship first, rather than having gotten physical right away.