Safeguarding the roof over my and my son''s head

Hello. I''ve been separated from my ex-partner for a year now (we were never married). Our son (aged 8) and I remain in the house my ex- and I bought together and my ex- has a room in a house-share nearby. My ex- and I have a mortgage together and we''re tenants in common (I think!) with a 66% (me) /34% (him) share as I contributed double what he did to the deposit. He''s been paying me his share of the mortgage payment (% not defined though - I think he thinks he''s paying half)plus some maintenance towards our son. My problem is that he''s drinking very heavily (almost every day as far as I''m aware)and it can only be a matter of time before he loses his job, which means he won''t be able to pay his share of the mortgage or maintenance, and will become homeless as he won''t be able to afford to rent. There''s also the distinct possibility that he''ll try to move back in. Is there anything I should be doing to (a) prevent him moving back in should he lose his job/rented accommodation (b) safeguard my and my son''s right to live in our home (if indeed we have a right to do so). None of these financial arrangements are in writing (apart from the tenants in common agreement)so I suppose there''s always the possibility that he could also just stop giving me any money towards the mortgage etc. I''m not in a position to ''buy him out'' unfortunately and would struggle to pay the mortgage on my own, presuming I could even get a mortgage. I currently receive no other benefit apart from Child Benefit.
Any advice anyone could offer would be very much appreciated! Thanks

As you are unmarried the starting point is property law and the deeds. Cohabitants cannot make financial claims against each other. In some circumstances it is possible to make claims under the Children Act 1989 for property to be made available for children until they reach maturity. The law is complicated in this regard and you really need to see a solicitor sooner rather than later to find out where you stand and what options there are.

If Child Benefit is the only benefit you''re receiving, have you looked into Child and Working Tax Credits?

The last time I looked at the qualifying criteria, single parents would need an income of around £60,000 before they received nothing at all.

That extra support may be enough that you can be confident that you''ll be able to afford the mortgage on your own if the worst should happen.