Contagiara comes from the verb contagiar, meaning 'to infect' or 'to spread'. While it can refer to physical illness, it's often used metaphorically for emotions or ideas.
In
"Primera Vez" is DVICIO's breakup song, but not the angry kind. It's the morning after the decision has already been made, when the head has moved on faster than the body. The singer opens with the distance itself: "Hoy estoy más lejos de ti" (Today I am further away from you). He remembers a trip to New York together, proof this wasn't a fling, before landing on the line the whole song turns on: "Toda mi piel no está de acuerdo con mi decisión" (All my skin does not agree with my decision). He made the call. The rest of him is still arguing.
That gap between decision and feeling runs through the whole song. He once swore he'd grow old with her, and sings it plainly: "Yo que juré envejecer a tu lado" (I who swore to grow old by your side). By the chorus he's talking himself out of chasing it back: "No lo fuerces, no lo fuerces" (Don't force it, don't force it), a line aimed at himself as much as at her. The title fits because everything here, the distance, the doubt, is happening to him for the first time. He's guessing his way through it same as anyone would.