How would it sound if in the moment you said to her, "would you mind, I would really like to spend time with our boyfriend alone, could he come and find you in a bit? Thanks so much, I would really appreciate it." Then spend time with him and have him go to her and show her some attention so that she feels like she is appreciated and loved by him just as much. I would just keep doing that when the situation comes up. Maybe have him go to her first sometimes and then he can say I am going to find zenchaos now, so see you after that. That way she will come to understand that she isn't wanted in the moment, but that she is still loved and cherished.
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