I’ve fallen out of love with my boyfriend—the spark is gone—but the idea of leaving him makes me feel awful and sad. Do you have any advice, or has this ever happened to you? Being a teenager is really hard.
Keeping someone you don't feel for, is nothing but injustice. When someone leaves, it's because someone else is about to arrive. You should better serve him this opportunity than feeling pity for him.
Actually, love is rather a decision than a feeling. It is normal that feelings are very strong in the beginning and you will notice less intensity of emotions after a while.
In my opinion, a relationship has a goal: the marriage. So, it is about discerning if he is the right one. The right one will be a good father and husband, you have the same values, ideals etc...