My interpretation of the movie and Rick's suicide:
Just finished watching this and I really liked it.
Paul was trying to get a doorway into the lives of others and he achoeved this by feeling free to act how he liked and commanding/affecting situations, people and their lives. Rick learned of Paul's perspective during dinner (when he danced with Paul) and the subsequent park scene (where he had his first sexual encounter with a male).
When he got home, he wanted to share it with Elizabeth, but she rejected him and his story. She then mentioned that Rick was naive, just like his father***. Rick didn't seem to be able to handle this slight as well as the fact that Elizabeth wouldn't look at him afterwards. Rick had taken a leap of faith by confronting this new sexual experience and the feelings that it bought (excitement, freedom and nuance) but ultimately he didn't believe in this experience; nor himself. So he killed himself. Seemingly immediately, which I found to be very impactful.
I am open to any disagreement.... :)
***[Similarly, another character in the movie hated being likened to his father (the son of the doctor) and Even Ousia/Flans own children showed their rage at 'being born!'.]
Although Paul mocks Freudian theory (over dinner with Ouisa and Flan), the younger characters in the movie seem to show a lot of parent-related angst.