Of course its possible, a huge amount of people do it, but in todays society, it happens less often. I guess when people have it on offer they get curious, also we're more likely to marry later in life, meaning that on average we'll have more sexual partners. Many cultures promote 'no sex before marriage', these cultures will have a higher proportion of people who have only one sexual partner for life, but that's not always what decides it, if you find the right person at a young age then what the point of playing the field? You have what you're looking for.