I’m mostly interested in the girls as well, of which there are 7 possible matches (and 7 counterparts with the rest unable to be matched with), and I ly a couple guys have caught any interest from me. The rest are all diamond mines, but as yeti said leveling up the relationship status takes a while the more you achieve it. You eventually get 20 gems back and it goes up in increments of 5, but it’s really not much compared with how much everything else costs, even if you only spend gems on a few characters as I do.
The dev team seems to favor the guys by a lot in terms of which gender they create more characters for and who they make available. Which makes sense if you consider the typical player base and their preference for these kind of games. I do wish there was more of a balance between the guys and girls, but I realize that’s wishful thinking. At least it means more people to diamond mine off of, I suppose.