Hi Lorraine
Your boyfriend will need to pay more into his IVA if his earnings increase, but this must be offset against his increased expenditure. To calculate what each of you should be paying towards shared household bills, I suggest that you work out the percentage of earnings you both contribute as individuals, and apply the same percentage to all shared household bills including the mortgage.
There are few risks to you as a homeowner, if you are living with someone who is in an IVA - but do make sure that he keeps up with the repayments as failed IVA may lead to bankruptcy proceedings which will identify your address publicly. Whilst this should not affect your credit rating, this will be advertised in the local paper.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk