I don't know why everyone is asking why on earth the OP had a baby as if it's a decision that can be undone. Baby is here, can't be sent back, therefore the rights and wrongs if having a baby is irrelevant.
OP, if your partner is contributing financially and will still be staying with you when he is home then he is still classed as living with you and you'd still be a couple for benefits purposes as the separation is not likely to be permanent. Things they look at to help them decide whether you are classed as living together are:
- who pays the bills? Are any of them in joint names? (FYI, compliance officers are able to check things like utility bills to see if your usage of gas/electricity/water is consistent with the number of people you claim are living in the house)
- are you known locally to be a couple?
- is leisure time spent together?
- if he stays at the house, where is he sleeping? If you're not a couple, is he paying you rent?
They have a huge list of things to consider, all available on the gov.uk website for anyone who wants to read it, and from what you've posted you would fail virtually every single one.
Tax Credits will take a current year income figure from you. On the claim for twelfth you put your income from the last tax year but once it's sent back and on their system you just phone up and tell them that your income for this tax year will be an estimated £xxx and they'll amend the amount that you receive.
Are you definitely claiming everything you're entitled to? For childcare costs do you use a childminder or a nursery? Childminders are often cheaper than nursery and so long as you meet the minimum hours requirement you will be able to claim the childcare element of tax credits which can help with up to 70% of the costs. Are your outgoings as low as you can get them? Things like meal planning and going down a brand (e.g., swapping heinz for own brand) when food shopping can help. Call your utility companies and check that you're on the cheapest tariffs based on your usage, do an online price comparison for gas/electricity/phone to see if anyone can offer it cheaper. If you're paying back any debts then call the companies involved and see if you can negotiate a slightly lower monthly repayment, it'll take a little longer to pay it back but if you're struggling then you need the cash now, for example if you're paying £50 a month on a debt and your struggling explain it to them and offer £30 instead. Do you have any skills that you could use in a home job? People per hour and Lionbridge both free work from home opportunities if you have clerical skills, if you drive then you could look at freelance delivery work in your area (I know someone who does this and takes the baby with her), it might not be steady work or highly paid but every little will help.
Mostly though, keep going OP. It's not forever and it will get better if you keep plugging away, especially once your DP is qualified and can move into a higher paid job. When DH and I first started out we didn't have much and what we did have was almost all spent by the day after payday but little by little we kept chipping away and we kept climbing and improving and keeping on at it so that now we're comfortable. I'm not wiping my backside with tenners or eating my morning cornflakes out of a golden bowl but we have enough nowadays for the things we need plus the things we want. You'll get there too 