It may resemble certainty about what they want, but actually, once the limerence is over, the relationship almost always ends. The limerence causes you to ignore red flags because you project your own fantasy onto them. You can think you're compatible when you really aren't in reality, because of that fantasy. Once someone wakes up from it, they realize it wasn't all they thought it was. It also takes them away from reality, so that they're caught up in trying to revolve their life around someone who might not even reciprocate their desires, instead of building their life up in realistic ways. Even if there is reciprocation, it's something you build your life around only for it to eventually die off.