Sufriendo is the present participle of the verb sufrir (to suffer). It's a highly emotional word that conveys deep pain and anguish.
In this heartbreaking ballad, Selena uses it to express the intense torment of unrequited love. The line "Quizás me muera sufriendo" (Maybe I'll die suffering) is incredibly dramatic, perfectly capturing the feeling of desperation for a love that will never be returned.
In "Como Te Quiero Yo A Ti" ("How I Love You"), Selena brings Tejano warmth to a classic, painful situation: loving someone who simply will not love you back. She starts by admitting that her thoughts constantly drift to this person with "Siempre voy pensando, pensando en ti" ("I'm always thinking, thinking of you"), which fills her with joy until reality hits and she realizes she is alone. She does not sugarcoat her embarrassment either. She calls herself "triste y tonta" ("sad and foolish") just for wishing "Que tus ojitos me querrán mirar" ("That your little eyes would want to look at me"). Notice the diminutive -itos on ojitos here: in Spanish, it adds a layer of tenderness and longing, making the crush feel sweet even while it hurts.
The chorus hits with total honesty about this one-sided romance. She writes off her high hopes as "sueños locos, pura ilusión" ("crazy dreams, pure illusion") because she knows deep down, "nunca me vas a querer / Como te quiero yo a ti" ("you are never going to love me / Like I love you"). Things get downright dramatic toward the middle, where she fears she might die "llorando, soñando, esperando" ("crying, dreaming, waiting") for love while offering "Las cosas más bonitas de mi amor" ("The most beautiful things of my love"). It is blunt, melodramatic, and completely relatable to anyone who has ever held out hope for someone out of reach.