We can take our time
As writers, and adults, we might be a little scared of having our characters believe they've found "the one." Here's something that this song tells me that we aren't recognizing:
1. She might have actually found the one. The chances are slim for a sixteen-year-old to find the person that she really is going to live the rest of her life with but possible.
2. This song sets us directly in a young adult's mind set. Who cares if she is right or wrong. When a teen experiences new, young love, he/she believes that it is the "the one." Because it feels so right / deep / intense. These aren't reasonable assumptions to make as a teen, but guess what. Teens aren't always reasonable. If you have your teens overly reasonable when it comes to love, you've missed the mark. Somewhat reasonable makes your character likable, overly reasonable makes your character unrelatable to other teens.
So take it from these kids in Emblem3 as they're definitely in the right age range. It's okay for teens to believe they've found Mr or Ms. Right.