for "nightline," abbie boudreau, abc news, los angeles. >> polyamory. thanks to abbie boudreau for that. >>> just ahead, we're going to go to florida. shocking, never-before-disclosed details about who casey anthony says killed her child. [ male announcer ] lately, there's been a seismic shift in what passes for common sense. used to be we socked money away and expected it to grow. then the world changed... and the common sense of retirement planning became anything but common. fortunately, td ameritrade's investment consultants can help you build a plan that fits your life. take control by opening a new account or rolling over an old 401(k) today, and we'll throw in up to $600. how's that for common sense? and here's my depression. before i started taking abilify, i was taking an antidepressant alone. most of the time i could pull myself together and face the day. but other days, i still struggled with my depression. i was coping, but sometimes it really weighed me down. i'd been feeling stuck for a long time. i just couldn't shake my depression. so i

polyamory is a growing phenomenon. in the united states. experts say being poly is not for most people. >> the primary issue for these polyamorous relationships is jealousy. jealousy and possessiveness. that's very human nature and hard to fight. >> reporter: a modern family in truly modern times. abbie boudreau, abc news, los angeles. >> fascinating. >> know what polyamory means, many, poly, amory, love. kind of like you. >> oh, see, now that is what i'm talking about! that, oh. >> keep that up for the rest of the show. >> keep it up for the rest of my life. >> they said, the main problem in these kind of relationships is you get jealous. we would hate to see the girls get into a cat fight over you. >> put the picture back up, guys. that is just. >> he's dreaming. >> oh, that reminds me of a very, very good dream. oh, lord have mercy, thank you. some dreams do come true. >> wonder how your girlfriend would feel about that one. >> we'll be right back. >> keep dreaming. >> uh, uh-uh. ♪ skinny ♪ so skinny >>> i'm still w

. >> reporter: in the world of polyamory, where the more the merrier, all are free to date outside of new relationship, we bring another person in. and the magic is, i have new relationship energy with ian and all these chemicals. when i come home to john -- >> reporter: no longer an old shoe at that point. >> no longer an old shoe. >> getting polished up a little bit. >> reporter: but later, he admits he does get jealous at times. >> it can be tough. especially like when i said that little voice and that self-esteem comes up. or that social voice, of that's your girlfriend. >> reporter: some people watching this might think, these people have no self-control. and this is all about sex. >> it's not like we've slept with hundreds of people and it's this crazy sexual thing. >> reporter: and if you're wondering about their sleeping arrangement, they each have separate rooms. even a planned schedule for intimacy. >> i actually like scheduling it because i can look forward to it. >> reporter: polyamory is a growing phenomenon. researchers say they are nearly 500,000 polyamorous households