Helen and Rob were shagging before we learnt about Jess, I think, but to be honest, I can't remember.
I think the whole CM thing is going to send him off on one, and he will end up taking it out on Helen, probably when she sensibly says something like, "Well, just take the DNA test to put an end to all this," now it's the authorities involved, not just Jess, and he'll punish her for not being supportive. I suspect he has convinced himself that the baby isn't his, and that she really has been shagging around, because otherwise he has to admit he's screwed up and the world doesn't actually fit the model in his head.
Or possibly Kirsty will witness something between him and Helen, and will pull him up on it, and he'll threaten her. Either way, I suspect his behaviour will be more threatening as he loses control and things don't go his way.
It wasn't clear to me if Rob was there when Peggy was telling Tony she's changed her will, or if it was just a mother-son chat between the two of them alone (although during the party). So while Rob knows she's talked about changing it, he may not yet be aware that she's actually done it.
BTW, I came across this -
www.networks.nhs.uk/editors-blog/ambridge-to-get-its-own-health-budget