I just heard an answer online about how people fall in love... apparently there must first be an attraction then an obstacle and then when that obstacle gets removed (e.g parents, or distance), then the passion can occur. It seems like a very easy recipe to falling in love.

Some(me) might see that the obstacle is a tension.

The man in the interview goes on by answering why there are so many sexless marriages and say that the reason is because the intent of the passion has already been fulfilled(think flower and bee).

So i am guessing that couples who stay together have somehow managed to figure something out or they are completely sexless

Some stay married because of the children.
I think my mothers obstacle before she met my stepfather was her previous marriage.
In some way i feel as if my stepfather(who has been married to my mother for decades), has used her previous children as a type of obstacle in order to always have something to move from the road.

So maybe that is how they renewed they`re marriage?