Mi hermana trabaja por mí porque estoy enferma.
My sister works for me because I'm sick.
Yo no compré esta comida para ti.
I didn't buy this meal for you.
Ese libro romántico es el mejor para ella.
That romantic book is the best for her.
Queremos viajar con él porque él conoce bien la ciudad.
We want to travel with him because he knows the city well.
Ella no nos invita a nosotros porque no somos buenos amigos.
She doesn't invite us because we are not good friends.
Catalina no baila con ellos cuando ponen música lenta.
Catalina doesn't dance with them when they play slow music.
When the preposition con (with) is followed by the pronoun mí, it becomes a single word: conmigo. Notice that the accent mark disappears when – go is added. Conmigo is translated as “with me” and must be used whenever con is followed by mí. The same thing happens when con is followed by ti. Contigo means “with you” and must be used whenever the preposition con is followed by ti. Here are some examples:
Tú debes comer conmigo porque yo sé cuáles son los mejores restaurantes.
You should eat with me because I know which are the best restaurants.
Ella no quiere bailar contigo. Ella quiere bailar con él.
She doesn't want to dance with you. She wants to dance with him.