The trope applies when a lesbian identified character is shown in a sex scene (explicit, implied or alluded to) or in an intimate/romantic scene with a man, for whatever reason.
The storylines vary, from the lesbian characters having doubts or questioning their sexuality, to sexual assault, or the characters trying to get pregnant (which then segues into All Lesbians have Kids Trope) and the showrunners seemingly unfamiliar with alternative methods.
TV shows also use various plot devices that all ultimately achieve the same result: the lesbian character is depicted in an on-screen sex scene (often enjoying it) with a male character or shown interested in a male character (often in the case of PG shows). These plot devices range from dreams, body swaps, mind melds or alternative universe scenarios.
The trope can also apply to storylines that aren’t romantic or sexual in nature, but in which the character is still paired with a man, either as part of a joke, played for comedy or forced with a man as part of a fake marriage/fake dating scenario: the end result being another lesbian character whose storyline involves a relationship with a man (real or not) instead of with a woman.
The list below does not take into account instances of lesbian characters having male love interests before they were labeled or identified as a lesbian (the number of male love interests for lesbian characters on screen is otherwise higher than indicated below)