Sufocar means 'to suffocate' or 'to choke'. It's a powerful, dramatic word that adds a layer of urgency and desperation to this romantic song.
When the singer says "Beija-me, não quero sufocar" (Kiss me, I don't want to suffocate), he's using it metaphorically. He's not literally running out of air, but expressing an intense, almost painful longing for a kiss, as if he can't breathe without it. This poetic hyperbole makes the feeling of desire incredibly vivid and memorable.
This song by Portuguese artist Paulo Sousa is a huge, dramatic declaration of love. He starts by saying that if it were easy to speak, he'd just sing his feelings instead: "Se fosse fácil falar / Eu dizia a cantar" (If it were easy to speak / I'd say it singing). He feels an unstoppable pull towards someone, comparing himself to a river flowing to the sea: "sou rio, tu és mar" (I'm a river, you're the sea). It's a beautiful way to say he feels like he's destined to be with this person.
The chorus is a desperate plea for affection. He feels like he's in trouble and needs her to rescue him with a kiss, singing "Diz que é hoje que me vais salvar / Beija-me, não quero sufocar" (Say that today you'll save me / Kiss me, I don't want to suffocate). All he wants is to be held and never let go, in the one place he feels he belongs: "Por entre os braços onde eu só quero estar" (In the arms where I only want to be).