FICO has nothing to do with income
FICO score (and I’m sure it’s the same with all the rest of them) has nothing to do with income.
It’s not factored in, by law. So’s your age, race, origin, and much more. The federal law that regulates the credit information prohibit it.
The only information that goes into your FICO score is information that’s on your credit report. There’s no income there…
As to opening another card and not using it – that won’t help to build credit history because it will be reported as inactive, so…
If your boyfriend is good with credit he can open the new CC and make only small purchases on it. That may actually help.
Just make sure NEVER to be late on payments.