The Monogamists
Plot:
Carrie is spending all her time with Mr. Big, and then finds he's not being exclusive, which she can't handle. Miranda has broken up with Skipper, but when she sees him out with another woman, she tries to get back together, on a non-exclusive basis, which he can't handle. Samantha goes apartment hunting, supposedly with a realtor on an exclusive basis, but actually continues to use others.