A character’s bisexuality is established in sweeps season for a limited number of episodes, and then dropped immediately from the storyline. When ratings need a boost, often a straight or ambiguously bi female character will kiss another woman (usually a tertiary character or one-episode guest star). The long-term implications are generally negligible and the female regular characters are almost never shown or mentioned being attracted to another female again.
The non-regular’s remaining screen time in the series will generally be measured in minutes rather than hours or seasons. Introduction of this kind of brief bisexual storyline to a show is mostly just a ratings stunt, calculated to get more viewers while creating a manageable amount of blow-back from straight audiences or network censors. Sweeps episodes air in February, May, July and November, the periods when advertising rates are set, based on the ratings received by the programs shown at that time.
Several characters who were shown in one or more “sweeps” lesbian kisses or hook-ups are not included in the lists below: Rachel Green, Ally McBeal, Susan Mayer, Quinn Fabray, Rory Gilmore, Carrie Bradshaw, and more. The full list can be found here. Additional reading: Sweeps Week Lesbian Kiss