Some interesting questions I don't think we really can answer. I figure Dimitri didn't sleep with Rose because I don't think they really have that urge or get pleasure from it ( well i'm sure they is some factor of pleasure) but i think Blood is the ultimate desire and pleasure factor. So i don't think it was a big deal for him and plus, the whole living forever thing, i think they have more patience and a better look at the bigger picture. Sadly, it's not for positive means just for the betterment of themselves. Even though Dimitri may be soulless, they still retain their memories and what they once used to feel, which is probably why he wants Rose to join him or dead. He doesn't want that bitter reminder for all eternity.