Here's the absolutely, positively, ultimate reason, I promise*, why I won't regard Rose to be the Doctor's one true love of his life(ves): I think it's bad storytelling, because there're only two directions it could go from there on.
- The Doctor never loved like this before and never will again. I hope and believe this character is going to be around for a long time still, and to go all that time without love while having the capacity is very, very sad. But the longer the character lasts - given that new people with their own ideas get put in charge of the character all the time - the more this direction is not going to happen. Now that the Doctor's fallen in love once, someone else will want to do it their way. So:
- The Doctor loves again. But, the way the relationship with Rose has already been built up (and continues to be built up even though it's past), it's too late for it not to be cheapened by the Doctor loving again.
I never liked the development (and I think that, all along, this though unarticulated was the reason why I didn't), but now that it's there it oughtn't have that happen to it. Yet, if the property lasts, that can't be avoided. The reason I must believe it wasn't what the Doctor believes it was is that, in the end, it won't have been.
* subject to change without notice