Things that friends do:
-Hang out all the time
-play video games together
-make each other laugh
-Always help and be there for each other
-love each other
-support each other

Things that couples do (besides the ones above):
-Hug a lot
-kiss
-piggy back rides
-live together
-say they love each other all the time
-go on trips together
-share clothes
-wear matching tee-shirts / hoodies
-compliment each other
-have sex

Things the Sidemen do:
All of the above.

...

Except maybe the last one, well at least that we know of...