Homosexual relationships are also possible, as there are games with no specific gender lines ("all pairings").
There are also Girls' Love games, which focus on female/female relationships, and Boys' Love games, which focus on male/male pairings.
Dating sims such as Tokimeki Memorial, and some role-playing games with similar relationship based mechanics to the genre such as Persona, often give choices that have a different number of associated "mood points" which influence a player character's relationship and future conversations with a non-player character.
These games often feature a day-night cycle with a time scheduling system that provides context and relevance to character interactions, allowing players to choose when and if to interact with certain characters, which in turn influences their responses during later conversations.
As you get to know better, the lady will become horny, allow you to take-off her skirt,... Now you just need to figure out a way to have sex with...
[more] You wake up in a strange land, not knowing where you are or what happened. [more] Two close girlfriends are alone in a room, and they are both getting horny.
There are many variations on this theme: high-school romances are the most common, but a dating sim may also take place in a fantasy setting and involve such challenges as defending one's girl from monsters.