Primaveras literally translates to "springs" or "springtimes". While it's a common word, its use in this song is particularly poignant and metaphorical.
Gloria Trevi uses "las más bellas de las primaveras" (the most beautiful of springtimes) to represent the best years, the most vibrant moments, and the most joyful periods of life that the man lost by choosing the wrong woman. It's a beautiful and evocative way to express the depth of his mistake and the preciousness of what he forfeited.
Have you ever seen someone make a really bad choice in love? Gloria Trevi's song "Él Se Equivocó," which means "He Made a Mistake," tells that exact story. It's about a man caught between two different women. One woman is genuine and transparent, giving him her love freely and standing by his side no matter what. The other is the complete opposite: she's calculating, demanding, and manipulative, pretending to be something she's not.
Faced with a choice, the man picks the wrong person. The singer, who is the woman left behind, declares that "he made a mistake" by choosing "the bad one, the one who didn't love him, the one who deceived him." She's heartbroken, but she's also sure that he will eventually regret his decision. She believes that one day, he will realize he lost something truly special, like "the most beautiful springs" and "the fullest moons," and he will cry when he finally understands his terrible mistake.