Let's take it we are talking about being "in" love. I have heard that humans, like some animals, are "programmed" to be "in" love for 2 to 3 years... just long enough to meet, fall in love, feel secure, have kids and give security to the family. Then it all goes downhill.

I have to say I think this is probably true. By then ,. however, we are so far in that it's difficult to get out ( joint home, bank account, friends etc.. )

I personally would like to go through life with a series of realtionships that last only while that strong passion lasts. The problem is once that has gone you are so deeply entwined in other ways it hurts like hell. I have recently had two break ups.... one was a relationship that had lost all it's passion, but had lasted years and years. The next one was still passionate, but we were incompatible. I tell you what, the long term one hurt like hell when it came to the break up cos we were so entwined in our lives.... families, friends, business, home. Horrible.