Can I keep Joint Tenancy Despite Ex-Partner Still Floating Around?

Hello I am a Joint Tenant of a 2 bed Council Property. My ex-partner(joint tenant) ditched me and moved to America with our son and new boyfriend whom she is now married to. She has been gone now for over 2 years. My worry is that she may one day return and try to re-access the property with her husband. She may even be pregnant or have had another child in the 2 years. Would this give her a good case to re-enter the property and if so, what would the Council want me to do? My reason for staying in the property is that it is a place that I would like to have access tom my son if/when she returns. The Council have so far said they have no objection to me remaining in the propert and have accepted she is no longer living there. I now recently have a new partner but we are not yet living together. Please please help as i feel the clock is ticking and I am unable to decorate or feel at home as longs as this matters remains outstanding. Thank you.