without this sounding too much like a love in between me and krustyman, i agree with him - just because the dad has a new family dosent mean he'll just want to abandon his old one. Seeing your dad by internet is hardly satisfactory. You say it's time for you to be happy now, but does your son want to go to australia? can your partner come here so that your son still has a relationship with his dad? clearly i dont know what your family situation is like, and you may well feel you deserve a new start but dont forget, you chose to have a child by this other man, and that means you have to do everything possible to mean that they have a relationship, in fact you have to work harder at it seeing as you are the custodial parent..
again, what if your exes partner ha been in, say, thailand, and he wanted to take your son there to live? Would him saying "well you can communicate by internet" been good enough for you?