The word love gets bandied about an awful lot, and by none more than those young people experiencing those grown-up feelings for the first time. It's powerful and heady stuff to realize that you've finally discovered what all of those songs and movies are about. The first time you tell someone to whom you aren't related that you love them marks a moment when you start thinking of yourself as an adult (whether you actually are one or not that's a different article).
What most people remember about their fist loves is as much the passion and confusion with which that time was fraught as it is how things actually were with the object of their affection. It lends a power and a glow to something that, 10 or 15 years later, would likely have been a decent relationship (or worse, a really crappy one). It was subject to none of the stress of full-time jobs, child raising, and retirement savings. Subject those golden times to the processes of buying a home or a major car repair and they would quickly reveal their true colors. It's hard to admit that the upheaval you felt inside of yourself through adolescence made blew so many things utterly out of proportion, including those feelings.
It's lovely to look back and remember the person who taught you about hiding love notes in pockets and handholding on the bus. It can certainly bring warmth to your heart remembering how innocent and beautiful those feelings were. There will probably always be a place in your heart for that person, because their remembered self is as much a part of you as you are a part of them. But that isn't love, it's nostalgia. It's quite true to say that fond remembrance never dies.