I like reading romance, she likes reading science fiction. What book can we read together?

Answer 1

Look into Sharon Shinn's books. I especially recommend _Archangel_ and its sequels.

If she likes fantasy as well as sf, try _Kushiel's Dart_ and its sequels (I forget the author's name). Warning: there is some explicit sex in these -- but if you're reading it together, that might be a plus.