According to some Namesake comic fans, the following conversation between Emma Sr. and One suggests that he had been involved with Daniel Crewe at some point:
On the other hand, One found and raised Daniel:
It would be little weird if he'd been romantically involved with him, given that. That said, while I doubt One really "loves" anyone, emotional abuse and manipulation are definitely in his vocabulary.
Was there ever any romantic relationship (however one-sided) between One and Daniel?