Contravía literally means "against the flow of traffic" or "the wrong way" on a one-way street. It's a fantastic and visual word that you don't hear often.
In this song, the singer laments, "No vi la señal de que iba en contravía" (I didn't see the sign that I was going the wrong way). He uses it as a metaphor for a relationship doomed from the start, perfectly capturing the feeling of realizing you were heading straight for heartbreak.
Ever felt like your heart was just too delicate for this world? That's the whole mood of this song. The singer takes all the blame for a breakup, saying, "No me pidas disculpas, que la culpa es mía" (Don't ask for my forgiveness, the fault is mine). They admit they fell for the wrong person and completely missed the warning signs. The main idea is that their heart is just too sensitive, or as the song says, "frágil" (fragile).
Because of this, it was easy for the other person to break their heart. The singer wishes they could be different, wishing for a heart like their ex's, someone who seems to have no feelings at all. They sing, "Quisiera ser como tú, como tú, sin sentimientos" (I wish I were like you, like you, without feelings), so they wouldn't be hurt by lies. But they can't change who they are, and the song ends with the painful admission, "Pero no soy como tú y aquí sí me estoy muriendo" (But I'm not like you and here I am, really dying).