Factually speaking, addressing the continuation of the reply that I missed, we don't know how Bruno described his feelings to Nemesis because that wasn't in the narrative. We don't know if she's even aware that the "aisuru mono" is Gallerian, or if that's just the impression she got from his behavior, and none of this was told to her at all.
If Bruno himself said it, it'd be one thing. But he didn't. And we don't know what he said.
As for "koi", mothy has used that in situations where it would be (presumably) one-sided (like with Irina and Kiril, Kiril being in love with Elluka at the time). So there's that.