"My boyfriend of 2 years is starting up a new business and has contracts lined up to be started in the next month or so. So he should see payment by end of Q3 this year."
What's he been doing up until now to earn money - and what is he going to do in order to earn some money between now and the "next month or so" when the contracts start?
Why will he not get paid until the "end of Q3" - i.e. end of September? He should be billing on a monthly basis for work completed (depending on the business, even on a weekly basis), but even this means that work done in June and invoiced at the end of the month probably won't be paid for until the beginning of August. How does he intend to fund himself and the business until then?
What happens if the contracts fail to materialise or get cancelled? What happens if they don't pay on time, demand a discount or simply don't pay?
Although you won't say how much he's asking for, let's assume that it's at least 4 months rent plus the same in total for child support, bills and living expenses. So somewhere between £5,000 and £10,000??? What about the cost of running the business - transport, materials, equipment, insurances etc?
This has better be a bloody good business if he's going to be earning enough to cover his current outgoings (rent, bills, child support etc) and the outgoings of the business - and pay you back anything more than a few hundred pounds a month.
"He isn’t able to get a bank loan as he can’t show income for the past year."
So you've already been subsidising him for a year - and now he wants you to "lend" him whatever savings you have left? Have you actually seen any of these contracts? How much are they paying? If no more than he'd get working somewhere else then it's not financialy worth the effort.
As for taking a share in the "business" be very wary of doing this. If you become a co-owner you might also be liable for the business debts - e.g. if he runs up debts for materials, VAT, income tax, on a business credit card etc.