She fucked some other guy after me?

My girlfriend and I have been together since about November 2020. And not till now almost two years later she tells me in the heat of an argument that she fucked some guy after me. And I know who he is, he’s always popped up since before she told me that. And I feel lost as to what I should do, she says forget about it and continue how we are now, like damn bitch I’m processing everything rn, it’s been a week or two and I don’t know how to feel, I can forgive her but she gets away with it. And I can continue as if nothing happened. But literally after her and I met the next day she fucked that dude. And what hurts the most is that I had to find out now after a baby, after planning our futures after all of that. Smh any advise on what I should do next?
She fucked some other guy after me?
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