In my philosophy class, and an interesting question was posed by my professor: is it love or nostalgia? Sometimes we get so caught up in our emotions and endless memories, that we tend to confuse love for nostalgia and nostalgia for love. In reality, we are just so obsessed with the past because memories tend to shape us and our future decisions. The thing is, we also tend to distort our memories and remember specific parts in each memory. We unconsciously pick out the good and bad from each moment.
You've experienced what might have been a crush or a love, nonetheless, as much as you'd hate to admit it, you've learned and grown a lot from that phase. You might have never thought it would be a "phase" but it just somehow unknowingly ended up that way. With you calling it a phase. As you go on with your life, meet new people, learn more about yourself, you will find yourself remembering detailed moments from the past. You'll find yourself unconsciously smiling at things like you did in the past when you were uncertain of the future, uncertain if everything in this world has an expiration date.
It's love when you miss the unnoticeable nuances in them; the way you both communicated. When the flaws in them weren't noticeable enough for you to feel distant, uncomfortable, awkward, or (in a bad way) different with them. They weren't toxic: sometimes making you happy and sometimes making you hate your life and yourself.
It's nostalgia when you are reminded of them solely by the feelings you had in your memories. You are trying to make yourself believe that you miss them, when in reality you just miss that time when you both went to the beach and unexpectedly, because it was so windy, all of the balloons flew away. You miss being happy in that moment, you miss the raw humorous times you shared. You miss not feeling lonely.
There is nothing wrong with wanting good company and good memories, but it is definitely important to be aware of this distinction, since believing that your first love is the "one" cannot be deducted by memories only. We remember the happy moments, the good times that remind us how "perfect" that person was. What about the tough times? Why are we not nostalgic about the times when we were hurting? This is when it's fully noticeable that you are missing the good memories that actually made you happy and vibrant, not the person.
Nostalgia is quite terribly funny, it has enough power to backtrack a person and pull them away from moving on to better things. It has the power to confuse a being with something as passionate as love and hate. You can make yourself believe that you miss a person a lot when in reality you just miss the times when you were smiling and enjoying the moment.
It's love when you are fully aware of the tough times and you both still love each other through such hardships. You need them, not just their presence or company. We are all different people, but it's love when you miss a person for the person they are--their flaws, low and high points, their personality, the mention of their name and the way they speak. The things that make them, them.