It seems to me from Tati's video that she was annoyed that he never promoted her vitamins or had her on his channel after all she did for him. She probably felt used but annoyed me by constantly saying 'my love for James wasn't transactional' but it all kicked off when he promoted a different vitamin instead of hers. She did clearly have monetary expectations on their friendship. She also cried at the end when saying 'this isn't about money', that was the only time she cried. It seems to me that it was about money. She finally used him to promote her vitamins though, she has gained millions of subs in a few days. She got what she wanted from their friendship.
Also to add.. not watched James or Tati videos, this is just my opinion as an outsider.
She doesn't care that he flirts with straight men, she cares that he didn't promote her product.
He refused to promote her vitamins 'because his subscribers were young'. She was OK with that.