Camping proposal scene – what movie

The only thing I can remember about this movie is a scene where a guy and his girlfriend are camping. He tells her he found a cancerous spot on his back, and when she goes to check, he’s written “will you Mary me” on his back (obviously he had no cancer). If I recall… The movie was quite sad despite the odd proposal. And someone in the movie could have been a doctor or dermatologist (a friend or a main character) help!!