The girl is not "got stolen", they just play game that if the mc is believe and loyal to his gf now ex and really reject this cool looking girl that like mc cuz she got saved by mc when she was little and she see the mc having a gf and for whatever reason when this 2 girl talk they make this game cuz the gf girl is a lil bit of a red flag (wanna have perfect bf while somehow not considerate abt the boy's feeling).
Also, mc is like a rope getting pulled all direction and getting tangled without a care in mind and just letting it all go like that, and is not the "good" or "make sense" kind of mc. He basically almost enjoy this if he really wanna get involved with anything like this (he is what i will categorize as kind isekai mc protag level of making me irritate the hell out of his action and decision, like got convinced to not killing an assassin trying to kill you and now the said assassin is doing it again but now there is a damage being done level of kind. HE IS KIND! ALMOST TO THE POINT OF SUICIDAL)