Temor translates to "fear" or "dread". While "miedo" is a more common word for fear, "temor" often carries a slightly more formal or profound sense of apprehension, making it a bit more evocative.
In the song, the singer expresses, "Porque tuve temor / Que no me hiciera caso" (Because I had fear / That she wouldn't pay attention to me). This reveals a deep vulnerability and the emotional stakes involved in confessing his feelings, making "temor" a key word to understand his hesitation.
Julian Mercado's "Cuando La Vuelva A Ver (En Vivo)" is all about a guy who's kicking himself for not telling a girl how he felt. He admits, "ayer no le dije nada porque tuve temor" [yesterday I didn't tell her anything because I was afraid]. He was scared she wouldn't pay attention to him or listen to his voice.
But he's not giving up! He's determined that "cuando la vuelva a mirar, voy a decirle todo" [when I see her again, I'm going to tell her everything]. He wants her to know "todo lo que yo siento aquà en mi corazón" [everything that I feel here in my heart]. He's so serious that he says "si pone condición voy a aceptar pero ahora ya estoy que muero" [if she sets a condition I will accept but now I'm dying]. He's ready to accept any terms, because he's absolutely smitten and can't wait to tell her how much he loves her.