I personally don't see an issue with the speed but I do see an issue with the flaunting it so soon. Even if Tan and Jim had split far before the public knew that you'd think he and Sarah would want to keep it a bit private for a while.... if it weren't for her wanting the social media punch and him, it being all he knows. I feel that a lot of this may be driven by the desire to banish Tanya from being associated with him, coming from Jim himself maybe but definitely for Sarah's sake. She comes off very insecure about Tanya, what better way to make it all about them now.
Jim is too old and boring to be a lad about town so his place in the market is wedding planning, how to be a new dad etc, I mean, his fans were teen girls, being a guy out on the pull was never going to sit well.
As for the pair of them in general, she behaves like a 16 year old, hanging off him, it's childish and embarrassing. No wonder Tanya grew out of that. Sarah posted a picture of some jeans, he commented 'Cute. I approve' - my boyfriend said this to me, I'd tell him to duck off. Approve?!
Tanya just grew up and he didn't like that she was no longer totally dependant on him I feel.
As for Tan, I bet she has got/had a new man, she just isn't parading him like some prize, using him to stay relevant. She's learned the lesson of over exposure. She's held herself unbelievably well throughout this really (except tik-tok maybe). She's obviously emotionally broken but she's been pretty dignified. She's an 'actress' now, not a lifestyle vlogger and her content fits that.