Hiya, I worked for WhiteLabelDating, so have a bit of experience, but take my views with the usual grain of salt.
1 - The dating industry is an interesting one. While nominally you are helping people find the person they will be with for the rest of their life... this doesn't help you for repeat sales... it also doesn't really match the usual reality.
So, for keeping people coming back there are a number of possibilities.
Firstly, if you provided a great matching service... people will come back eventually anyway. After all, the majority of people won't find their perfect match the first time... and while it may take a few months, people will often end up as a single again several times over.
Secondly - and a little more on the dodgier side of dating - you could position yourself in a niche in which people err "turn over" a lot more quickly. Such niches can be highly lucrative - if less moral. "maritalaffair.com" or "sugar daddy" are "good" examples of this genre.
Thirdly - you can build a community by providing other features that people will come back to see... I'm not sure exactly what these could be... but WLD had forums and other community-building online features. You could think of things like setting up meetup groups so that nearby singles don't just hook up and leave, but become friends with other singles, and stay a part of the community.
2 - For you or for your customers?
For you: cashflow. Followed by conversion-rates. Followed by signups. Followed by hits. ? :)
For your customers: being happy... setup a feedback page and ask them.
3 - You have a awesome male/female ratio. Don't worry about it too much.
50/50 is optimal, of course, because everybody wants to have as many options as possible... but 60/40 isn't too bad. For some of the sites I've seen, a 90/10 ratio was a good day, and most of them were skewed far more than yours.