Thanks for your question.
In the event that you cannot afford to pay him off for the monies paid for the extension the onus would be on him to establish an interest in the property.
If you are unmarried, his only option would be to make an application to the Court to claim an interest in the property under the Trust of Land and Appointment of Trustees Act. You can do this for the type of money he has spent on the property if it has increased it's value.
However, he would certainly need a solicitor to make the application for him because it's quite a complicated area of law. He would have to pay their fees. If he does nothing then you have absolutely no problem at all because nothing would happen. The onus is on him.
If he is able to do this, and note this would take at least months, he would then have to litigate on how/when he is to receive money. He would have to make an application for an order for sale if there was no other option, but the accommodation of the children would be a very important concern of the Court.
It's not going to happen as quickly as you might think so you should try and relax a bit. Litigation in this area takes a long time.
If you can show that you have been reasonable and can pay a proportion of the monies owed with the balance to be paid at a later date then the chances of the court making an order for sale would be considerably reduced. He may instead get a second charge on the property which you can repay later.
If this has been useful please kindly click accept so that I may be rewarded for my time. If you do not click accept your money stays with the site and I do not receive any credit for the time I have taken to answer your question.
I will answer your follow up questions you may have.
DISCLAIMER: Answers from Experts on JustAnswer are not substitutes for the advice of an attorney. JustAnswer is a public forum and questions and responses are not private or confidential or protected by the attorney-client privilege. The Expert above is not your attorney, and the response above is not legal advice. You should not read this response to propose specific action or address specific circumstances, but only to give you a sense of general principles of law that might affect the situation you describe. Application of these general principles to particular circumstances must be done by a lawyer who has spoken with you in confidence, learned all relevant information, and explored various options. Before acting on these general principles, you should hire a lawyer licensed to practice law in the jurisdiction to which your question pertains.
The responses above are from individual Experts, not JustAnswer. The site and services are provided “as is”. To view the verified credential of an Expert, click on the “Verified” symbol in the Expert’s profile. This site is not for emergency questions which should be directed immediately by telephone or in-person to qualified professionals. Please carefully read the Terms of Service (last updated February 8, 2012).