Who was Cersei supposed to marry before Robert?

While Cersei was promised to Prince Rhaegar Targaryen as a young girl, he ended up marrying Elia Martell before being killed by King Robert Baratheon — Cersei’s eventual husband.

Did Robert ever love Cersei?

King Robert Baratheon did not love Cersei, even a bit. He, in fact, called her Lyanna during their first night together, causing Cersei to hate him as well. She continued her incestuous relationship with Jaime and bore him three children – Joffrey, Myrcella, and Tommen (passing them off as Robert’s).