I'm I the only one?

Thinking that the two characters in "In the mood for love" might have slept together?

Yes the ambiguity stays, but consider this.

1- In one of the last scenes, Maggie Cheung's character tells Leung'S character, finally, after she refused earlier, that she "don't want to go home tonight".

2- Later in the movie, after Singapour, we learn that Cheung's character lives with a child in the appartement she used to occupy with her husband. No trace of the husband; did they break up? And who is this child from? Why wouldn't her husband take care of him? He might be dead, but also he might have learned that this child was not his...but Leung's one. Also, why would Cheung pursuy Leung to Singapour, call him, and then hang up without speaking, but to tell him something she realized at the very last moment was better kept secret?

All those possibilities are, I think, proposed by the movie. But no one can be sure.