Fracasara comes from the verb fracasar, meaning "to fail." It's used here in the imperfect subjunctive, which often expresses hypothetical or uncertain situations in the past.
In the song, the singer admits, "Tenía miedo de que fracasara" (I was afraid that it would fail). This reveals a vulnerability and past hesitation about love, making the arrival of a new love even more impactful. It's a word that conveys deep emotional stakes.
Grupo Arriesgado spend this song on a man who had stopped expecting anyone. He says so in the opening two lines — "No te esperaba / Llegaste en medio de la nada" ("I wasn't expecting you / You arrived in the middle of nowhere") — and then gives the reason: "No quería amar a nadie / Tenía miedo de que fracasara" ("I didn't want to love anyone / I was afraid it would fail"). The waiting had already been done, and it had come to nothing: "Toda la vida había esperado a alguien como tú / Pero no llegó" ("All my life I had waited for someone like you / But they didn't come").
The chorus makes the big promise — "Sobre cualquier circunstancia yo te elegiría" ("Despite any circumstance, I would choose you") — but the line that stays with you is the smallest one in the song, and it closes both verses: "Que cada vez que frotes tus manos / Sientas que faltan las mías" ("That every time you rub your hands together, you feel that mine are missing"). It is a gesture you make alone, in the cold, without thinking about it, and he wants to be the thing it is missing.