Wait, what?! But Aeran has a romance bar in his profile. Where did you read this? If this is true, this hurts me on so many levels, but also makes me not feel slightly guilty that I spent time with Veyer.
Not all companion characters are LI but there are characters that are not part of the main gang yet can be romanced. There also will be characters with whom you can just flirt with or have one night stands with, without them being really LIs. So yeah, just because you can sleep with someone, they might not be romancable.