Jack and Ally's physical relationship is often shown.
There's some nudity in the film, mostly when Jack and Ally are sleeping together, which is shown to varying degrees but not completely explicitly. Ally is seen completely nude for a split second as she's getting out of a bathtub, which the pair appear in naked together on occasion, and there's a whole lot of kissing.
(Just another warning, a HUGE spoiler is in the next slide. Skip over the next photo if you'd prefer not to know a major part of the film's ending.)