Hi Jak, I've thought about it, but I simply can't find any title.
Which female lead is so silly that she gives in to the vying of a second male lead, despite the fact that she already loves the male lead, and even dates him? Why would she cross over? Perhaps if she's suffering from a narcissistic personality disorder?
The love triangles I've seen consist of a male lead who's acting cold against the female lead, and a second male lead who isn't afraid to show his feelings.
Could you give us an example that fits your description?