Vedavati

Rama asked Agastya, Please tell me more. Where did Ravana go after this?
Agastya said There was a beautiful maiden called Vedavati. Fair and pure, she was praying in the forests to get Vishnu as her husband. Ravana passing by saw her and wanted her.
Seeing a guest, Vedavati greeted him and gave him a seat. Buring with passion, Ravana asked Vedavati who she was.
She said was the daughter of Kushadhwaja and the grand daughter of Brihaspati. She was born when her father was reciting the vedas, thus she was named Vedavati. She wished to have Vishnu as her husband and was thus praying to him.
Ravana said Why go for a dark God as your husband when I am there. Vishnu is shrewd.
Vedavati said It was not proper to say such words about Vishnu.
Ravana then grabbed Vedavati by her hair and tried to pull her towards him.
Vedavati escaped and jumped into a blazing fire. She said She would be born again and would be cause of Ravana's destruction. In that birth, she would get Vishnu as her husband.

Vedavati was then born as Sita, who got you, Rama as her husband. It was because of her that Ravana died.