Mujeriego directly translates to "womanizer" or "player". It's a very common term in Spanish used to describe a man who has many casual, romantic relationships.
In the song, the singer confesses that his past life on the road made him an "indolente, un mujeriego" (an insensitive person, a womanizer) who had given up on love. This single, powerful word perfectly captures the classic "reformed bad boy" story, setting the stage for how meeting this one special person changed everything for him.
Ever felt so burnt out on romance that you completely gave up? That is the exact mood at the start of Llegaste Tú. CNCO and Prince Royce admit that life on the road turned them cold and careless: "Dejé de creer / Me hizo un indolente, un mujeriego" ("I stopped believing / It made me indifferent, a womanizer"). They were totally shut down until this one specific person walked in and flipped the script overnight.
Suddenly, the cynicism melts into pure infatuation. The track hits you with that sudden shock of catching feelings hard and fast: "¿Qué está pasando? / ¿Qué estoy sintiendo? / Que así de violento / Yo me enamoré" ("What is happening? / What am I feeling? / That just this violently / I fell in love"). Using violento here describes the sheer intensity and sudden force of the crush. From crowning her "la más divina del Instagram" ("the most gorgeous on Instagram") to refusing to let go of her waist on the dance floor ("no me despego de tu cintura"), it is an upbeat, catchy celebration of how fast love can take you from feeling totally down to simply saying "wow."