When I had "the talk" with my husband, I used this kind of elaborate metaphor to describe my feelings about monogamy, and he liked it so much he's used it to explain our marriage to other people...
Imagine you're shown into a wonderful room. In this room are all the things you love: every video game, book, album, movie, whatever it is for you. All the clothes in the closet fit and are flattering. The bed is soft and comforting, like it was designed for that crick in your neck. You love your room. You love it so much, in fact, that you might never leave. And not leaving is fine. You can stay.
Then imagine that someone says to you, "do you love this room?" And of course you say "oh yes, this room is lovely." And this someone says, "Well, if you want you can stay forever, but if you ever put so much as one toe outside the door, it will lock behind you and you can never ever come back."
That means that in order to stay in the room, you agree that you will never play any other video games, read any other books, wear any other clothes, sleep in any bed other than the ones in that room. Meanwhile, you can look out the window and plainly see that there IS life outside the room - you just can't be a part of it.
That's monogamy. It's not that what's in the room isn't appealing. You love the room, and everything inside it. It's that you're voluntarily saying "I will live in one room forever." So my husband and I decided to go ahead and take the locks off. He's still my room, and I'm still his. But, to belabor the metaphor even further, there is now the possibility for adding rooms to the house.
Anyway, that's my take on it. And it worked for us.