Child benefit

[Cldad]

My partner and I separated one year ago. We split 50/50. She is pregnant with a man 20 years her junior due in 7 weeks. She says can’t look after kids overnight as too much strain. I now have them 7 nights and she looks after one weekend day and 2-3 afternoons after school until I pick up after work. She has always received the child benefit but I said I am going to ask for it as I’m looking after 7 nights. She is very angry at this. She doesn’t work and it’s all she gets, (she has been spending the money she received when we separated for last year)
I am not asking for any maintenance money as she doesn’t work. This current situation will go on until at least mid December which she says is temporary and shouldn’t change. I can see it being much more long term.
Am I being unreasonable asking for the payment to switch to me while I’m looking after 7 nights a week?

You're not being at all unreasonable. I suspect the reason she'll be angry is if she's claiming wider benefits as a family - CB isn't a lot on its own, but if you have CB you can claim for universal credit based on having a child including a housing element for a 2 bed (if it's one adult one child)
If she doesn't have CB then she'll only be able to claim UC as a single person, which is a very small amount towards rent (far less than the rent costs, usually) and a living payment as a single adult (around £75ish) a week

None of that is your problem but bear in mind it would be such a drop in income for her that she may fight to have the child(ren) back full time

I strongly suggest you start gathering evidence of having them, whether it's texts with your ex confirming any arrangements, drop offs, school runs you've done etc, in case she disputes your right to claim CB. If you have location data on your phone you might find you've got more a digital footprint than you realise which can really help!