Ya know......I basically did the same thing as you bro

it finally took another girl to convince her that it was totally over........and lord behold, several days later I found out my ex was bisexual and she was sleeping w/ a girl behind my back.
She could've told me and I would've been supportive

aaaaanyways.....good luck with that though. It doesn't sound like theres a whole lot you can do to make things better other than continue to be civil and a friend if thats ok in your eyes.
Hatred is gained as much by good works as by evil. - Niccoló Machiavelli