I'm not a huge fan of this kind of ultimatum, "go out withme or no more life energy". Not only Yukiko can probably found another person for that but forcing her hand like that don't put her in a good mood.
Me neither. But I could see this coming from the first few chapters. Remember that this is the same manga that we expected to only get to kisses and then threw a relatively explicit sex scene.
The author also it's setting an erotic mood for the interaction of this chapter... Kinda to indicate that MC enjoys it.
Right now there's only two ways out. GF comes to rescue or GF decides to "fuck it all" and get em both a food source.