a bridegroom of blood: The context suggests that this statement was part of a circumcision ceremony.
Circumcision was the cutting of the foreskin of a male child. It may reflect an older custom among some Semitic peoples (ancient groups from the Middle East who spoke related languages).
Among some groups, including certain African communities today, circumcision is performed at puberty rather than in infancy. If that were the case here, the phrase may connect circumcision with marriage or adulthood.