If you like 2 people at the same time, always choose the second, because if you would've wanted the first so badly, you wouldn't have even noticed the second.
Or not. We're designed to be social, to be surrounded by people and the fact that our hearts are controled by chemical impulses is surely not helpful either.
Maybe there are many pheromon smelling individuals out there. And maybe there is more than one perfect guy for me. And I get the chance to meet them all until I make a choice.
Or it's simply that one guy you know you shouldn't have, though you want him so much, therefor you seek refuge in the liking of other guys, hoping that eventually, you will stop liking the first one.
So it's not the second over the first, but the first over the many.