Thank you for your question
My name is Clare
I shall do my best to help you but I need some further informtaion first.
Can you prove that he was only a lodger and paid nothing more towards the property?
Was the Declaration of Trust Registered at the Land Registry?
Has you registered the Declaration of Trust it would have been impossible for your ex to try and overturn it at this late stage unless he could prove that he made a subsequent contribution
However since you did not it becomes a little easier for him to claim that in fact the agreement was changed when he returned to live with you.
Again had you had clear evidence that he only gave you the sort of rent that a lodger would then you would have easily been able to dismiss his attempts to argue otherwise.
As things stand whilst he would have some difficulty in overturning it he has more chance of doing so - although I still do not think he has a particularly good chance of success
Please ask if you need further details