she met this dude online and she found out that they have a lot of things in common. To my surprise, she revealed her identity to him and now they're "friends". They talk a lot and she tells me about it and now she's now entertaining the idea of messing around JUST ONCE with him to satisfy this newly discovered side of her because she never went through anything like this growing up because she was an angel.

Has she been transparent with him about being in a relationship? Also....how would her past matter?

Why did you mention in the beginning that she came out as bi a few years ago? How's this relevant to this current story?

Why did I give her? Because I feel like I need to pay for my mistakes. I cheated on her once on our 2nd year and I couldn't live with it for a while.

Oh boy....yeah, tell her exactly how you feel, and then enroll in counseling.