Huh?
I never have this problem before.
Probably because i dont give a damn. 
I mean this have never crossed my mind, like worried that the
person's gf/bf thinks im disturbing their gf/bf.
Just go ahead and make friends, dont worry too much. If your
intention is to make friends nia, you wont be paranoid. Unless you
have some other motives.... But even if so, fret not. Dont flirt
too openly can liao when the partner is around.