How can they call them self's there bestfriend,when they sleep with there gf/bf?

I dont get how some ppl can say oh he's my bestfriend,when they sleeping with there best friend..gf/bf..and still have the nerve to act like nothings going on,and still be like ,yeah he my best friend...How can they still have the nerve to say that they are,when they obviously arent...Girls that sleep ith there bf bestfriends are HOES...and guys that sleep with there best friends gf are dawgs...