"Cosas De Novios" is a song about a situationship, and it says so right in the hook: "Hacemos cosas de novios pero no somos nada" (we do couple stuff but we're nothing). Every weekend the same call comes in. She feels lonely and despechada (stung, heartbroken after someone let her down) and wants to share his pillow. He is not complaining.
Matt Hunter plays it cocky. Her other admirers are "incontables como sus esmaltes" (as countless as her nail polishes), which is a funny little image, and he waves them off with "tus pretendientes son baratos y yo soy caro" (your suitors are cheap and I'm expensive). Watch the dropped letters: pretendiente' is pretendientes and to' is todo, the way the words really sound when sung fast. Me pones bien mal is not "you make me feel bad" here. It means something like "you drive me crazy", in the good way.
The second verse gets more heated, with her sneaking away from a boyfriend ("aunque tiene novio conmigo siempre se escapa", even though she has a boyfriend she always slips away with me). The last line keeps it honest: "Ella sabe que no somos nada" (she knows we're nothing). No promises, no drama, just the weekend.