Mordelón is an interesting and somewhat playful word derived from morder (to bite). While it literally means "biting" or "nipping," it often carries a connotation of being a bit feisty or playfully aggressive, especially when referring to a kiss.
In the song, "un beso mordelón" suggests a passionate, perhaps even slightly teasing kiss, rather than a gentle one. It adds a touch of playful intensity to the romantic sentiment, making the kiss sound more exciting and memorable.
Have you ever been so in love you just want to become one with the other person? That's exactly what Luis Miguel is singing about in "Amorcito Corazón"! He's got this huge crush, a "tentación de un beso" [temptation of a kiss], and he wants that kiss to ignite in the warmth of their great love. He just wants to be "Un solo ser y estar contigo" [a single being and be with you], dreaming of a future together.
This song is all about that intense, passionate desire to be completely united with someone. He wants to tell his love, "Decirte mi pasión por ti" [tell you my passion for you], and he imagines them as "Compañeros en el bien y el mal" [companions in good and evil]. It's a sweet and direct declaration of love, promising that even time won't weigh them down. He's sure his "Amorcito corazón" [sweetheart darling] will always be his love.