I cheated on my girlfriend, now what?

I've been losing interest in my relationship for a while and I told her but she wanted to keep trying to I felt guilty and said ok.

But hey, I guess I'm selfish and a girl approached me at a party and after some drinking I ended up having sex with her.

I haven't told my girlfriend yet. What do I do?
Tell her, apologize and break up with her.
Vote A
Tell her, apologize and ask for forgiveness.
Vote B
Don't tell her, but just break up.
Vote C
Don't tell her and act like nothing happened.
Vote D
Select age and gender to cast your vote:
I cheated on my girlfriend, now what?
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