Earlier on in this incarnation the Doctor had met a beautiful woman. She was of royalty, rich in both taste and culture, and as far as culture goes 17th century France is high on most lists. Sure, Pothay in 62nd century gives it a run for it, but 17th century France has and will always be classic. Madame da Pompadour was everything that Rose was not.
The Doctor had fallen for that queen. She offered him a different type of relationship and in fact a different type of life. Madame da Pompadour had offered the opportunity to truly settle down and it had been tempting. Oh, it had been very tempting and the Doctor had let himself believe that it was time to just accept it because with Rose a future could never be simple. He had been at a crossroads and never got the chance to live out his fantasy because the Doctor had gotten the time wrong. He had arrived too late. Madame da Pompadour passed away with him on her mind.
Matt had been Rose's fantasy. Unfortunately for her, Rose didn't arrive too late for his death, she was there. Against her better judgment she had almost sacrificed her life for that bloke only to be pushed away as he did it for her. Rose was really shaken after returning to the TARDIS. She walked past him that night and despite his best efforts, she didn't talk about it at all. Rose would wake up the next day perfectly fine like nothing had happened. Everyday she was becoming more and more like him.
The Doctor shrugged it off. He knew exactly how Rose felt about him, but she knew nothing of what his feelings were for her. The Doctor didn't even know that himself. She had asked him in many different ways over there times together and every time he found a way to dodge the question. During their early travels Rose didn't seem to care as much, but after Martha left and Rose returned she was wiser and older and wanted an answer. After the events in the hills of 1849 California Rose had made that certain.
It was only an eventual fact that in their travels another Matt would come along. Rose would fall for that simple life again, but he couldn't blame her. After all that's exactly what Madame da Pompadour was to him way back when. The life of the wandering traveler seeking adventure was the Doctor's life. Rose couldn't live that life forever. She'd either be tempted to leave through the heart of another man such as Matt or would die taking matters for herself. Both of these possible time lines worried the Doctor immensely. It was why he had never made a decision on how he felt about Rose despite what his hearts told him. He couldn't let her know no matter how much it frustrated her because this was no game, it was life.
The Doctor sighed standing in the console room alone. If only there was someone out there in this great big universe that could understand his dilemma and the pain that surfaced under it. Till then it was the same old life moving on whether Rose was in the TARDIS or not because she was just a companion. She could never be more...