Legal Question in Real Estate Law in Illinois

Part of the problem you are facing is that the property was never legally the buyer's property. In order for a deed to be valid in Illinois, it must be recorded with the county recorder of deeds.

The boyfriend can sue you, but it is unlikely that if he does he will win. A landlord (which you actually were because of the "buyer's" failure to record) is not responsible for work the tenant has done on the property unless the work is necessary for habitability or the landlord is responsible for under the rental agreement. Since you did not have a rental agreement, unless the work was necessary (such as repairing code violations) you are not responsible for paying for them.

Sounds like the boyfriend was not on the contract. If that is correct, I cannot see any way he could succeed in a lawsuit against you (though stranger things have happened). If anything, he could try to get money out of his ex-girlfriend, but I doubt even that would be successful.

I think that you might have some exposure under the theory of "Quantum Meruit", as you would have benefitted from the work that he perforned without paying for it. Not likely, but possible.