I hate it too !
What is your game about? ? Who is the protagonist?
Male protag is dragged to a remote island resort by his girlfriend with 2 other couples. The relationships between you and the girls are point based, but so are your girlfriends.
This isn't what it will look like, I'm just working on the playthrough with backgrounds and sprites. Craig is a 'event' partner for Amy if you're not on the Amy path for example (higher points with one of the other girls). If your points with your girlfriend reach 0 it will be more apparent that she's flirting with the other guys, but it it goes below 0 she won't even attempt to hide it, at which point you can choose either the sharing or NTR paths.
Influenced by games like The Adventurous Couple and Deserted Island Dreams (but hopefully with better graphics/dialogue).