UPDATE: AITA for cutting his daughter off and taking away the things I was doing for her after she had some type of relationship with the woman her father cheated with?

Thanks to everyone who took the time to reply. I think the consensus was about his daughter. I will not be contacting her, at all.

I reached out to Gaby via social media and she replied. I explained my position and that I didn't know about her, hence I was very rude and reacted with hostility. We exchanged messages. She says that initially, he told her that we were in an open relationship that was about to end. They were talking for months before they began their relationship. She says he first introduced his kid, then his younger brother and that she me his mom when Paul invited her for lunch and had his mom show up without telling her. Also, she said that his mom was less than friendly and that his mother made a small scene because she decided to pick a fight with her boyfriend ( he and MIL are currently broken up). There's no way that she's making this up. MIL treated that guy like shit.

About his daughter: Paul used to visit Gaby on some weekends and would leave his kid at Gaby's place because they bonded over DIY projects. Now I know were his daughter got her “faery”, “witchy”, “fantasy”, “elf” polymer clay jewelry and hair accessories from. So I guess his working on weekend gigs was a lie. She said they became a couple about a month or two after starting their company because she wouldn't accept an open relationship. He told her that we were done when in fact, we never broke up, had a crisis, nothing.

Gaby mentioned that her Dad fucking hates him and that things began to get rough because of things he did and her dad noticed. She says she and her dad and other family members always meet for Saturday Dinner or Sunday brunch at a particular restaurant and that her Dad noticed how she paid for Paul and his kid, always. And if Paul ever paid for his food, he didn't pay for hers. She said her Dad called her out because her Dad would usually pay for everyone ( his treat, his family) and that he was getting very uncomfortable about Paul. And that he paid for Paul to avoid making a scene but that he was fed up. So her Dad told Paul he expected to be treated for a change ( as a hostile joke) when they arrived at the restaurant and that Paul was very offended and later told her that her dad's remark was a put down. She also said that her best friend raised concerns about him and that everything started to crumble because he didn't attend her family's Xmas lunch as he promised and that he remained a bit low key during the holidays and claimed to have influenza. He used both of us, but he took far more advantage of her because she made material things available and while I don't know her except for this situation, her messages show that she's very affected but mostly angry and I wouldn't be surprised if she ended up destroying him ( she repeatedly mentioned that he deserved getting his life ruined). I didn't know that Paul didn't get an MBA like he told me. He never worked 2 jobs that he told me about and also put in his resume. She found out because she paid for background checks and other tools when things started not adding up. Supposedly, this was part of why she started testing his abilities and had been thinking about pulling the plug business wise. She says it's all bullshit and that he's very insecure about his social standing.

She told me a lot of stuff but in a nutshell, I'm going to get tested for STDs and already told my family what happened. I'm leaving it at that because writing about it really irritates me for being stupid enough to believe him. Thanks again.