Obsidian voluntarily chose not to do a romance because they feel if they did attempt a romance, they wouldn't do it justice - due to the enormous effort and cost it would take to develop it, at the expense of exploring these other "mature" themes that don't necessarily deal with romance.
In lieu of a romance Chris Avellone actually would prefer to write a hatemance, and he made a short go at it on Alpha Protocol. Really though, I think the best "romances" were in Alpha Protocol as essentially, except for one case, they were dealt with in a mature and theme appropriate manner with very little emo-teeny bile-inducing dialogue.
...o noes, I'm discussing romance again. ICK.