What is going on and what should I do?

I have been with my girlfriend for almost 3 years now and the last 3-4 months have been the absolute worst. Every move I make seems to piss her off, every word I say seems to be fighting words, she is genuinely disinterested in sex, doesn't want to spend any 1 on 1 time together and has been talking to some random dude on TikTok. We have a kid together and another on the way and I have done everything I can to fix this I don't know what else to do.
What is going on and what should I do?
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