The questions are wonderful and have been asked by poets for centuries. People in this country often seem to feel that when we feel that exciting, first flush that that is love. That feeling is so exciting but not long, lasting.
True love is much quieter and much deeper than that.
You may no longer feel fireworks anymore. That does not mean that you no longer love your girl/boyfriend. It may mean that your feelings have changed and deepened.
If you look at her/him and feel peace and calm and contentment, this still could be love.
You need to go back and ask yourself what was love for you before. What made you decide if that was real? Now what has changed?
Now ask yourself what, exactly, do you feel now. Is it disgust? Is it nothing? Is it friendship? Are you attracted to other people?
If you still can't imagine yourself with other people, but no longer get butterflies when you see her/him, it may still be love.
You are the only one who knows what will satisfy you. If you need to always have fireworks, and there is nothing wrong with that desire, make sure you are okay with shorter-term relationships.
If you want a life partner, look inside of yourself and decide what will make you happy, not just today or tomorrow, but 20 years from now, too.
You are not "suppose" to feel anything, except happiness, everything else is individual.
Enjoy the searching.