[That doesn't particularly sound like someone Lavi would have been in love with either, though he notes the acknowledgement of a close relationship there. However, that matter is one he can at least leave until a little later, whatever his current suspicions on it might be.]

So she betrayed your trust after you offered her something that important. It sounds like she was plenty bad enough herself. [Shun's moral compass may not exactly be the straightest thing around, but personal betrayal is something he holds as a particularly immoral thing to do. Partially because of how much it's affected him, but also just because abusing that kind of relationship just feels wrong to him.]

I don't know her, but there's probably two options there. Either she spoke without thinking and didn't have time to regret it, or she wanted you to hurt and didn't care what she used to do it.