You asked and so I shall answer.
Yes, it could be “when you can’t live without them and your heart stops when they walk in the room” but really it’s so much more than that. Puppy love, crushing, passion, marriage. Love is a feeling.
Love is the moments. When time stops for you two. Whether they're looking at you or you’re looking at them or a two way street when the world melts away. When the scene, the issues, the good or the bad, simply don’t matter because all the comfort and safety you need is THEM. Whatever that entails, from strangers to friends to something more. Love is something you can feel, not something you can objectify. Love is how the moment matters to you. Not to the oblivious friend on your right or to the knowing friend on your left, but to only you. When a glance is so much more than that and even if it isn’t, it is to you.
Love is the experience. When their face is the only thing that you can vividly remember because it’s the only thing that you want to. The memory of their smile is brighter than the crescent moon outside your window and it keeps you up even more. When their name is the first thing you think of in the morning and the last thing you wish for at night. You re-play every conversation like a broken record but you don’t care cause you broke it yourself. Love is their voice being the only song ever stuck in your head and no matter how much you hum it it sticks. When secretly you don’t mind it. It’s when you lie to your friends about them because it's not something you want to flaunt like you would a crush. Its personal.
Love is the fire. If they love you, it's the best thing in the world. The importance of them to you and the fact that you are the same to them. When you are in a mutual state of love, you know. It’s not something three words can express. Or five words. Or one-hundred. It’s a feeling only felt by those in it and only understood in the same way.
When they don’t love you, its your part in it. It’s when you know who they love and the fact that that person won't love them like you do but you bite your tongue and bear it cause you love them just that much. Its when you know that they don’t know who you even really are but you smile and offer them gum and math homework answers because your motto has become ‘maybe someday.’
Love is when you know all that lies at the end of the road of your love is heartbreak, but you don’t even try to avoid it. Maybe it’s self-destructive, or stupid, or reckless, but it's all you can do. When you know that nothing good with them is coming for you but you honestly don’t care because you have a goal, and a goal it’s going to stay. Love is when you’re not even attempting to get over them because they are such a fixture and enigma in your life that you don’t care. The feeling has overtaken you. It’s love.