A real relationship (that lasts more than a couple of weeks) has many small touches to keep it going.
It has demonstrations that you care, and are thinking about them.
Picking flowers, going out to dinner, doing things together, all let your loved one know that you're thinking about them, and that they are important to you.
Sex is just the icing on the cake.
The problem is that none of those make for good gameplay.
At best, it's cutscene material, but D:OS 2's multiplayer focus means that cutscenes can't be used very often.
