Actually, Nicholas himself in his diaries has mentioned that he wondered how he could be in love with two women at the same time.
Young and/or inexperienced people tend to mix love with passion - I beleive this is what happened to N. too...
I share entirely your opinion. Most of people tends to mix them together (it's great that passion cmes along with love when you are in love...but without it, it could be mistaken as if it was simply love). It seems a little confusing, I know. But I think that this was that happened with Nicholas. But when Alix became a real possibility to him, when his father gave him permission to marry her, he put both, all his passion and love in Alix Von Hesse. And remained all his life a passionate lover of his own wife.
RealAnastasia.