Just a couple of observations: JWs are only supposed to date "with a view to marriage" ie not before they are of a legal age to marry and not as a social activity but quickly expected to commit or end the relationship. Secondly they are not permitted to date/marry non-JWs. It is highly likely your daughter's boyfriend's family are unaware of the relationship.
The only way he could legitimise the relationship, and even then it is frowned upon, is to get her to convert and get baptised. Beware!