I'm a little puzzled with DiDi's portrayal.
She seemed a lot nicer and a lot more innocent overall when she wasn't in a relationship but working on a crush on Sandra. When that went south and she shacked up with Matt, DiDi's suddenly become a rather nasty, selfish, dislikable person and the inability to get that orgasm has become her ONLY personality trait.
If I didn't know any better, I'd say that DiDi was getting derailed into the unlikable nymphomaniac to make no-longer-swinging-homewrecker-Zii look good all of a sudden...