Someone who already dives is best, but don't rule out that guy who's always wanted to dive, but just never took the plunge. You might be his motivation to go ahead and start something he's always wanted to do. I was a diver in waiting from about age 3. At 27, I finally got around to taking a class, you may find someone in a similar situation who becomes a die hard diver.
I recently met a lady who has always wanted to dive and planned to take a class with a friend, but that never worked out, then with her sister, but that didn't work either, then planned to take a class with her son, but he also backed out. We met, she signed up for class and our first date was shopping for dive gear. It's still early in the relationship, but she's certified and excited about diving and about becoming a better diver. Other areas of the relationship are also going very well. If I'd insisted on someone who already dives, I could have missed out on a truly wonderful lady.