Adrian is drowning in a sea of emotions right now.
Ever since Cassidy started singing and playing the guitar as if strumming his heartstrings along with it, he remained torn between approaching her and staying put there like a lovesick fool. He badly wanted to go up to that stage, pull her in his arms, and take her home with him. There were so many things that he wanted to do at that moment, but he refrained himself and chose to settle with his original plan -
To watch her from a distance, that is.
Adrian was not sure if Cassidy was only trolling them when she said she was going to serenade them, though. He was expecting a love song, but it ended up to be not like that at all. It's a freaking break-up song - some bittersweet music for the broken hearts and loveless souls.
Never romanticize alcohol, by the way! This is pure fiction ^_^
(I'm not even sure if this entire scene is romantic, to be honest - it's just 80% Adrian being a crazy mood, 10% angry Cassidy, and 10% chatty bartender)