I Can't Find a Book That I Particularly Liked Before and I'm About to Wear It! Urgent!

The male protagonist seems to be an actor and suffers from mental illness. The female protagonist is a psychiatrist introduced by the male protagonist's sister and is friends with the female protagonist. The female protagonist originally had a boyfriend. Later, the male protagonist's boyfriend and his sister went out for a picnic or something. In the end, the two of them seemed to be separated.