It's a natural part of growing up to develop romantic feelings and sexual attractions to others.
Romantic love is when attraction and closeness are combined.
Lots of relationships grow out of an initial attraction (a crush or "love at first sight") and develop into closeness.
We typically have shorter relationships as teens because adolescence is a time when we instinctively seek lots of different experiences and try out different things.
It's all part of discovering who we are, what we value, and what we want out of life.
And the kind of love we feel in romantic relationships is its own unique type of love.