Tesão is a Brazilian Portuguese slang word that refers to intense sexual desire or lust. While it can sometimes be used in a more general sense of enthusiasm, in the context of this song, it clearly refers to passionate, physical attraction.
Marília Mendonça sings, "Então acender ainda mais esse tesão" (So light up this lust even more), directly expressing a desire to intensify the physical passion between the lovers. It's a raw and direct word that captures the song's sensual theme.
This is a hangover song, dressed up as a love song. It opens with the singer getting home at dawn, asking herself "(é nós hoje?)" (is it us today?), the kind of question that only makes sense if the night before still has its hooks in her. Marília Mendonça trades verses here with sister duo Maiara & Maraisa, and together they turn one restless night into an entire chorus about wanting somebody back in your bed rather than in your life.
The evidence is physical, not emotional: "Na minha camisa, o seu batom" (on my shirt, your lipstick), "O cheiro do suor do nosso amor" (the smell of our love's sweat). She even asks herself outright, "Mas o que eu vou fazer pra esquecer você?" (but what am I going to do to forget you?), and every time the answer collapses back into the same four words: "Te quero pra mim" (I want you for me). It's less a plea to get back together than an admission that she hasn't moved on, however loudly she says otherwise.