Very little is opined about more than first love. That person will always be special for you. They'll have a place in your heart forever. And, to be fair, all that is true. You never forget your first love, the first person you shared with, the first person you opened up to. Unfortunately, or fortunately, depending on how you view life's picture, a first love is very rarely your only love.
Most likely, things just won't work out. That happens. You change and you both move on, hopefully amicably. Of course, things could be...messier. You realize they don't love you the way you love them and you have to let it go for your own good. Understandable. They may break it off with with you, leaving the ashes of someone bitter and broken. Also understandable, at least on your part.
The worst case, though, is first love severed by the sharp life of a short life. They were taken away from you, and unlike the other scenarios, you can never see them again. Ever, no chance encounters on the horizon. You could possibly blame yourself, and it would be easy to do so if the wound is too fresh and painful. How could this have happened? You thought you could keep them safe and you'd be together forever, despite how naive that sounds in retrospect.
No matter what the case, the loss of something so dear to you must hurt like no other. You're certainly not looking for a rebound. You could have even have sworn off love. After all, who's looking to be hurt — or hurt somebody again, because you're a time bomb and everything you touch dies? You were guarding yourself, understandably.
Then, they came along, and everything changed. It possibly took a little prodding, probably still is, yet you're falling in love again. Whether it's good or bad is irrelevant, because you can't stop it so easily.
But, perhaps, this person's second love is your, the new "interloper," first one. You want to heal their old hurts and some of your own, too, though it's not easy. How can you when they keep turning you away? Or what if you're living in the shadow of a lost lover? You can never replace them and you don't want to, so why does it still feel that way? At any rate, you're desperate to show them that you're your own person, not someone second rate.
First loves can be hard. Second loves can be even harder, no matter how sweet any rewards could be.