Is A Threesome Cheating

So my SO and I wants a threesome b4we get married! He says I get to pick the girl and contact her! He don't want any of her contact information! But I told him she has to get tested for everything even tho he will use a condom on her! But I told him I don't want him to stick his dick in her period....all she can do is give him blow jobs and oral me but I was wondering am i over reacting!  I need advice please ladies I want this to be fun but I don't want mess it up!! Btw I don't even kno where to find a person who would like to join us because I don't know anyone