Watson:

Wonderwall;

 •\ won-der-wall\•  [adjective]

Someone you find yourself
thinking about all the time, the person you are completely infatuated with.

• Harry Styles,
 you are my wonderwall. •

Sherlock:

I have nothing to say except:

Roses are red
Violets are blue
Louis is my kryptonite 
And Niall Horan is too.