Couple swapping ends in bisexual group fucking

These four met for a couple swap and the beefiest guy broke the ice by taking out his cock so the other guy's female could suck it. that's how things got lively and soon the four of them began to fuck together, rather than changing partners. the fact is that it occurred to one of them that they could also fuck each other, and suddenly the thing turned into a bisexual orgy where the girls were shocked to see how well the two guys had it together as if they were lifelong gays.