You'll be fine OP, it might take a while to get used to but you'll soon realise that it's very manageable. When I was married our monthly income was 4.5k. Now I'm divorced my monthly income is £1200 (including benefits) and that's for everything.
As pp have said, make a weekly meal plan and a shopping list and stick to it.
Shop at Aldi or Lidl.
Bake rather than buying chocolate and biscuits.
Don't let food go off. If there's leftovers in the fridge remember they're there and eat for lunch at the soonest possible opportunity. Apparently us Brits throw a third of our food away!
Buy clothes on Ebay or from charity shops.
Put a specific amount in a savings account each month for xmas.
Take picnics on days out, or homemade snacks and flasks of coffee.
Use box dye instead of going to hair salons.
Have less frequent haircuts, or consider using clippers on boys at home.
Toys on ebay can be mint condition and a fraction of the price of new ones.
Have a clear-out and sell anything you don't really use.
Have a monthly or fortnightly 'treat', whether it's lunch out, or a takeaway, or a trip somewhere you like.
Try cheaper skincare products if you use expensive ones. The Ordinary has done my skin wonders and is far far cheaper than the dermalogica that I used to use.
Use bar soap instead of shower gel.
Stop using fabric conditioner.
Dry clothes on a line or inside airer rather than using a tumble dryer.
I'm sure I've forgotten a few things but these 'rules' made my money stretch much further than I thought it could when I first got divorced. Good luck OP!