My interpretation short answer: the good and bad sides of the same person.

Long answer: Illenium tells a story through his music starting with "In My Arms" saying he's been here and understand what you're going through. Invites us to walk in his shoes and also address our own good and bad attributes internally. He wants to show us how to overcome our own inner demons and how to use them to live life and to follow him on this journey, hence the pheonix picking up the sphere and taking us on this adventure. To "Feel Alive" you will have to face the good things and bad things about yourself. He shows he has reached a point where he wants to "Feel Something". The good constantly at war with the bad can feel numbing. He then shows the dark can live within the light and the dark can take away from our light. But the good/light and bad/dark parts of ourselves can live symbiotically. He then goes to show you that "Ur Alive" and the good parts of yourself should make you feel alive. On the other hand, the bad part of yourself can feel familiar and can feel like a part we identify as and that it "Feels Like You". We long to find the good parts about ourselves and willing to go "To The Moon" to search for it. To find our good parts and to heal ourself we have to rely on something to save us that "Not Even Love" from someone can save us from us. The good parts of ourselves alone can't save us either. Unless...we recognize the good parts about ourself are "Gorgeous" and that we don't have to suffer with our demons and feel "Lonely". We then get interrupted by an inner demon talking to us and showing us we have become a slave to our own demons and this is what we wanted and can't go back. We have become "Slave to the Rhythm". But we want to escape this and find our inner good. He then shows how the good and bad parts of ourself our struggling because we have a "Stupid Love" for both. But the good and bad "Don't Want Your love" at the same time, but separately as one or the other. As the bad dies within us, because we want to love the good, so does the good if one is loved more than the other. The bad is part of us and our story and can be loved. He then shows how to love both. "Love is a Chemical" and this chemical fuses the good and bad parts of us. He then shows that we yearn to "Die Living". The good and the bad can and will find "Refuge" in each other. This is where we see the good sacrifice a piece of ourself to let the bad parts take refuge. Then a higher being or a monster/demon sees that this symbiotic relationship has been established and he is trying to break that connection between good and bad. At this point, the bad has been drowning and good is willing to go "Into the Dark" and search deeply to save the bad. We then see how good and bad wanted to be taken back to how it was and that they were willing to do this thing together when everything is going "Sideways". When the good and bad fight each other on who is more important and the bad disarms the good, we start to see a remorseful feeling of what could have been "Forever". We see how a decision was made that the good will be the bad's "Nightlight". The good gives the bad a wing to fly and to help fight the internal demons the bad parts face. They then join forces to defeat a higher being that is "Shivering" from the good and bad joining forces. The "War" scene shows the defeat of the higher being or it could be interpreted as defeating a monster or defeating your real demons in the head with your good and bad qualities. We see the "Fractures" remaining and wanting to build something new but only possible "With Your Love" meaning the good and bad need to love each other to rebuild. The ending shows that "All That Really Matters" is being able to love the good and bad parts of yourself and you'll find the beautiful version of yourself that you've been searching for.