The sound of 1st Base Runner in this song is also reflected in the video. Through mostly black and whites, some greyscale and a few flowers here and there this music is somewhat dark. It reminds me of an artist such as Finger Eleven or Hozier. In a more modern sense it can also have the same self awareness as an artist such as Flora Cash. It's just the type of song which when it is on- even if you hear it somewhere in public- you very distinctly know that this is the song which you are hearing.
For the most part a singer is sitting on a stool during this video while images of chairs and a house go by. I'm not sure why he wants to be the only one- it isn't really clearly explained as to who else he is in competition with- but this song is also somewhat short and feels like a bridge between two other songs or the greatness of an entire album. It has this way of starting and then just sort of fading out where it's not really your standard verse/chorus/verse structure, but it works.
I suppose that the want to be the only one can depend upon what your situation is in life or what you have been through and in that sense it can be left to interpretation by the listener. Maybe you want to be the best at your job. Maybe you want to be the best at sports or video games or whatever people typically compete over. But I think of it as wanting to be the only one for someone else. And in this video it almost feels as if he is not the only one because the other person has moved onto someone else.
I'm a firm believer that people need relationships outside of their significant other. Whether it be family, friends or co-workers, only seeing and spending time with one other person for the rest of your life would wear real thin real fast. But at the same time there is a way in which that belief can be conveyed which makes it feel less like "She needed more than me" and more like a healthy balance. So as I listen to this song and watch this video I don't know if it is possible to be the only one and maybe that's why this song sounds the way that it does.