I have to disagree with Hucksters normally great advice in this instance
What would your boyfriend do if you told him that after a valuation it turned out that you were in negative equity by £10,000 or £20,000 and that if you were to sell right now that you would each owe the bank £5,000 or £10,000? Would he cough up the money that he would owe or would he say he wasn't on the mortgage deeds and therefore he legally owes nothing on the mortgage.
Personally I think you need to ask yourself which of these answers he would give.
Legally, he has no rights and responsibilities on the mortgage and has never been entitled to pay a penny in return for living in the house. He has no responsibility for any bills that are not in his name and no responsibility for any debts that you have run up that are not in his name no matter whether they were directly for him or not!
And this is my exact point. From what you have said he has made little or no contribution to the house, the mortgage has been paid by you and so have the bills and you say that you have also kept him going constantly with financial aid. He has no legal right to the house at all, epsecially if you have given all this extra help and despite what some others contributors may suggest on this site the letter of the law stands and I have not heard of any other case where the property title owner has to pay compensation to anyone not named on the deeds unless there was overwhelming evidence that the non owner made a significant and majority deposit or mortgage contribution to the house. This does not seem to be the case here!
If he has a persistant argument I would ask him to evidence with documents and bank statements the direct payments and contributions he has made towards not just the house but also towards the running and maintanence of the house.
The mortgage lender will not chase your boyfriend if the mortgage is not being paid because he is not on the title deeds. He does not legally exist in their eyes.
I say be greedy and let him fight for what he wants, he is on the losing side all the way.
Unless of course you feel he should take something out of the house in which case I would follow Hucksters advice and speak to a mortgage adviser as you may not need to sell the house to pay him off.