Can he take my son away?

My ex wants to move 1000km's away and wants to take our son. He's in the process of taking me to court to have this granted. He is accusing me of being a bad mother, being an alcoholic etc, and getting an ex friend of mine that I used to live with to stand behind him. Admittedly I was only 17 when I had my son and found it hard to bring him up by myself when he left but I have never consumed alcohol in front of my son nor has alcohol affected my life (ie, I've held down a stable job for the past 4 years). My life was a bit unstable, (not alcohol related, just a young mum trying to support her son alone) but over the past 18 months I have picked myself up and now rent a nice 2 bedroom unit with my partner, we earn a good income combined and have never been in trouble with the law, taken drugs or anything of that manner. I am so scared of losing my son I don't know what to do. I have spoken to solicitors but I don't know if I can trust them with the advice they're giving me. I so far understand have the following in my favour: 1) My son was born here and all of his friends and family are here. 2) My ex seems to think he can go get a job at maccas and that will be enough to get a home loan. 3) I've taken my son off him before for dealing drugs. Does anyone know what he would have to do to succeed in taking him off me? Does anyone know if the court will take into consideration him slandering me? What should my solicitor be doing? I have a lot of friends who could write a lot of negative things about him, is it necessary? In my defence if I was such a bad mum my ex would have taken him off me a long time ago. I love my son more than anything and if he is allowed to go it will break my heart. Any advice would be fantastic. Thanks