How do we have a ?

Three girls, roommates, Cambridge uni, UK, 2 are dating, one friend. She is bi-curious so we said we'd help her but we don't know any 3some positions. Usually me and my gf peel off, she s like 4 times and pes out for a few hours, then I go on my friend, she starts off giggling but s fast but I feel guilty about taking advantage of my Gf's unconsciousness and I stop early. If this one is no good (4th try tomorrow) then it will probably be my last:( I do posses a 6 inch vibrator but the others don't know and there is only one. Be serious.