I've noticed that the happiness number doesn't go up even after all the sex scenes added ever since the variable's inclusion. I think when you decide to fix that, dev, I think a special quest for having 100 happiness should be unlocked or at the very least a special harem scene, it would be cool.

A sex scene doesn't increase the happiness variable, impregnating a girl does. And it's already possible to go above 100. 

I think there was a display issue somewhere, where the system itself wasn't able to show numbers beyond 99, but both the skillroom and the status->variables menu show the right values for me when I test it in the newest version.