I'm still under the impression that Namine really is in the same boat as Roxas in that I believe Namine actually existed as a separate person before the events that led to Kairi sharing her heart with Sora. Then again, I haven't completed Days and haven't been able to play Sleep so I don't know if that question has been addressed.
Personally, I don't believe either Roxas or Namine or Xion had any romantic feelings to express. No matter how desperate you are to turn every little subtlety into a romantic gesture, in the end you have to come to terms with the fact that none of them actually had time to even think about that. They were primarily concerned for themselves while their concern for others was understandably secondhand and had a lot weighing on their shoulders. No amount of wishing will change the fact that in fiction as well as in reality we don't always have the luxury of time wasted on romantic fantasy.
If Roxas had any feelings for Xion it was most likely inspired by familiarity due to the fact that the Xion doll was basically a clone of the keyblade wielder tying "her" to Sora, Kairi, Aqua, and Roxas (if for some only in appearance).