The drama that ensues from couple is usually caused by envy, mainly being one is not happy that the other get more attention. There are times when one of them realized he has found a better match in bed then his current bf during that particular moment, so when he immerse himself in this new found sexual outlet, the other is definitely not taking things lightly. Things are likely to get complicated when the one enjoying himself is the one that is initially against opening up the relationship to play together. The fact that he finally accepted the direction of the relationship, and starting to learn to enjoy himself, makes the other person uneasy and to a certain degree, jealous. Such is the drama that might arise if you choose to play with couples, so be warned!
But on the other hand, a couple who knows how to make each other happy in bed can certainly spice up the threesome when they tag team together to handle you. Let just say that, in those rare moments, you'll even consider having a three sided relationship, hoping that the sex can continue to be thus good every single time.