Before trying to find any answer, you have to know the question. And the question is not always so easy.
What is a relationship? Is it about love? Is it about sex? Both in equal ways? Or one more than the other? Somewhere I heard, that you have to choose the partner with whom you can live with, not the one whom you can not live without.
Many relationships go down the drain because...but hey, why? You break a relationship, you'll get a new one and a few years later you realize that you are in the same valley as you were before. Is love gone, when the sexual desire is gone? What do we call love? When you want somebody's body or when you want somebody's soul? But what to do with the mind? Is love possible without sex? Can you touch the other one, and the only thing you think of is having a good conversation with him or her? Maybe after 70. But at 20 or 30 or just less than 70? Can you have enough patience towards the stupidity of the other one, when you don't desperately want his or her body? But isn't actually the mind, that is wanting anything at all? We do feel sometimes, that the desire is somewhere under our belt area, but is it indeed? Our mind decides to like and want somebody. And we do indeed have very efficient organs to execute the demand.
We could maybe turn towards the direction, that everything comes from the mind. The mind wants, the mind hates. The only thing is, why the mind likes something and after some time gets bored or starts to hate the same exact thing? Is the mind insane? The mind is only an organ. Just like anything else, which we assume being inferior. But hey! Are they? Don't you just get the feeling that it's not your mind in control when indeed it is? The mind is in control, but then why isn't the mind controlling? Is the mind a floating thing? Does it go in the zone where there is some action going on?
And back to love. Love is the human mating season. That's how we call it. So you should mate till it's there. At a certain point, it will be gone and then you don't want to mate anymore. So pretty simple. Just like the mating season for the animals. A few weeks and it's gone. For people maybe it lasts more. A few months probably, but for humans everything lasts more, than for example cats, so it's just natural that the mating season is also longer. Otherwise, if it wouldn't be mating season, you couldn't have any logical explanation why after sometimes disappears like it would never ever have been there at all. For example, we love our parents. That love never changes. You just love them all your life the same way. But with boyfriends and girlfriends, the thing changes. Why? Cause it's the “mating procedure” involved in the issue. Sex namely. And when that gets on the rugged road... the doom day of the relationship is also not too far on the horizon.