I read in the New York Times that the US Congress is trying to fix the "Boyfriend loophole" in gun purchase restriction laws after domestic violence convictions. They note that individuals who have a "dating relationship" would also be included. To me, this sounds very vague, and the article also describes the difficulties lawmakers have been having with the definition issue.
I found this draft of the bill. Here is an except:
(a) DEFINING DATING RELATIONSHIP
(37)(A) The term ‘dating relationship’ means a relationship between individuals who have or have recently had a continuing serious relationship of a romantic or intimate nature.
(B) Whether a relationship constitutes a dating relationship under subparagraph (A) shall be determined based on consideration of—
(i) the length of the relationship;
(ii) the nature of the relationship; and
(iii) the frequency and type of interaction between the individuals involved in the relationship.
This seems to remain quite vague. Obviously this hasn't become law, but for the sake of this question, let's assume it does.