Rolear is a Spanglish verb derived from the English word "role." It means "to role-play" or "to act a part," often implying putting on a persona or trying to fit in.
In the song, the artist sings, "Para impresionarte también tuve que rolear" (To impress you, I also had to role-play). This reveals his effort to pretend to be someone he's not, highlighting the lengths he went to for someone who ultimately didn't care.
Have you ever tried to change yourself to impress someone? In "En Ti," the singer does exactly that, even starting to smoke just to get a girl's attention. He admits he knows she never asked him to do these things, but he's still filled with regret and anger because, in the end, she didn't care at all and left him feeling like a "chiste" (joke).
The song tells the story of a very public and painful rejection. The singer describes giving her flowers only to be turned down in front of everyone. The moment was so embarrassing that people recorded it, uploaded it to the internet, and even made memes about him. Now, hurt and humiliated, he curses her for the pain she caused and plots his revenge, showing just how messy a one-sided love can be.