how marriage happens: a dinner conversation

Oliver and I were the last ones sitting at the dinner table last night (typical) and this is the conversation we had:
O: "Mom, if you ever don't love dad and decide you don't want to marry him, you could just marry me."
K: "Well, that's sweet Oliver, but I've promised to live with dad and love him the rest of my life. And really, you can't marry someone that's in your family."
O: Mom, I just don't want to marry anyone.
K: Oliver, I bet when dad was your age, he didn't want to marry anyone either, but then when he was 23, he said to himself, "I sure would like to marry that Katie girl." And I said, "Pick me, pick me!"
O: So, you mean like, there is this group of guys and this group of girls on the other side and the guys are picking the girls they want to marry? (I guess I misled him a little with the "pick me, pick me" line.)
K: Well, sort of. People just kind of decide "hey you seem like someone I could marry, do you think we could spend some more time together?" And then if they do marry, they promise to be together for the rest of their lives.
O: Do you have to marry someone to have kids? (apparently, he wants one without the other)
K: Mmmm, not technically. I guess you could adopt kids.
O: So there are kids that parents don't want and they just put a sign on them that says you can have them if you want to be their parents instead?
K: Well, it's a bit more involved than that, (Do I get into the whole orphanage, foster care system, not to mention the world's neglect of their youngest?) but there are lots and lots of kids in the world who don't have parents to love them.

The conversation continued, but I'm wondering if he walked away with this: There are two groups of guys and girls and they pick each other like in elementary PE class. Then they get married and have kids. They could break their marriage vows and they could put their kids up for adoption.
And for now, he's probably decided he will be a bachelor with adopted kids. :)
He is five and he thinks more seriously about important issues than some adults do. In his five year old mind, marriage is as frightening as death. (These two topics come up frequently with him.)