As this song starts off sounding like Sheryl Crow, it finds itself taking a turn into something a little bit more country, with a bit of folk in it, and given the lyrical content it is best suited for this genre. There is this underlying sense in this song and in country music in general where it feels related to the blues. Sarah Segal-Lazar seems to have found it here and as this song is a breakup song it only makes sense for it to feel sad.
Right away lines like "We make plans for the future / but the end is drawing near" show how this is about two people who are together but no longer should be. There are specific events described in this song to show that it is about a relationship between two people, but I always like to take these ideas to a broader sense of life where you can just break up with a bad employer or someone along those lines but to where it doesn't have to be romantic.
This song just feels like it's about any time you have a passion for something and that passion fades. Yes, instances of a couple are here and so are lines like: "I thought this was forever but the signs were in the air". It's just that idea that you might have felt one way about something before but now you feel a different way and though unexpected it's time for a change. This can happen in life for various reasons.
Not living in Florida also makes me think of it as a vacation destination. The idea of Miami being cold (and, yes, Florida does get cold at times- I've felt it) just makes me feel like this also about that idea that you can go to a place on vacation and fall in love with it because you can have a magical time there but then deciding to live there is a whole other animal and it may not bring you that same joy. Either way, when it's time for moving on this song will hopefully help you go.