The girl - who's now 16 - told her school resource officer last month that 30-year-old William Forster raped her several times, beginning when she was 14. Forster is the boyfriend of the teen's mother.
The girl also told police that Forster asked her to send him inappropriate pictures of herself.
Forster was charged Tuesday with several counts of second- and third-degree rape, sexual extortion, sexual harassment, unlawful sexual contact and sexual solicitation.
He is being held at the Delaware Correctional Center in Smyrna on $36,000 bond.
