People with whom you have a financial connection can affect your credit rating as their financial circumstances could influence your ability to make repayments.
Just living with someone doesn’t create a financial connection — you need to have a joint loan, mortgage or bank account to create financial links. If you’re a guarantor for someone else’s loan, their credit rating or score will also affect yours as you’re promising to pay their debt if they’re unable to.
Make sure you regularly check your credit report to ensure all your financial associates/connections are correct.