Indomable means "untamable" or "indomitable". It's a powerful adjective used to describe a wild spirit that cannot be controlled or subdued.
In this bachata, Romeo Santos describes his past self as a salvaje (savage) but then confesses, "Y este salvaje no fue indomable" (And this savage was not untamable). He uses this word to reveal that while he seemed impossible to conquer, his lover's affection was the one thing that could finally tame his heart.
Romeo Santos lays all his cards on the table in "Tuyo", admitting that he let bad decisions get the better of him. He confesses right away: "presté mi cuerpo a extrañas no lo niego" ("I lent my body to strangers, I don't deny it"). He blames his past wandering on pure arrogance, explaining that chasing casual flings was just fuel for his pride: "Tal vez me alimentaba el ego y fue mi error" ("Maybe it fed my ego and that was my mistake"). To sum up that foolish wandering, he uses the word "desubicación" ("disorientation" or "being out of place"), basically calling himself completely lost for "alquilando mi piel" ("renting out my skin") while having the right partner right beside him all along.
Even with that blunt confession, the core of the track is a total surrender to the person he loves. Romeo insists that his days of acting wild are over, declaring "este salvaje no fue indomable" ("this savage was not untamable"). He promises total loyalty from here on out: "Me tienes amor, entero, todito, espíritu y carne" ("You have me, my love, whole, all of me, spirit and flesh"). Romeo brings his trademark bachata swagger into the mix, playfully asking "¿Y le gusta mi bachata amiguita?" ("And do you like my bachata, my friend?") before slipping into English to promise that he is completely, forever hers.