I know you are not supposed to discuss Hebrew Bible, but Biblical Hebrew here, so I am not sure if this is an actual Biblical Hebrew question. Could "bridegroom of blood" have actually have a literal meaning back then?
In Exodus 4:25 Zipporah circumcizes her son and says to him or Moses "you are a bridegroom of blood to me because of the circumcision." Usually people say she was talking to her husband Moses because she saved his life by doing the circumcision because
G-d wanted to kill him or the baby a few lines before because Moses didn't circumcize the baby earlier.
Maybe a circumcized baby has blood on it's private parts and a bridegroom who marries a virgin gets blood on his private parts sometimes? So, it might have been an actual term for a man who married a virgin. It is a wild guess, but it might be an ancient
_expression_ or just something she made up for the situation.
Maybe the baby was like a bridegroom who had blood on his private parts but from the circumcision. I may be wrong, but it is an interesting possibility.