Dear Woodywasp
You cannot do much at the moment, but take legal advice and keep a record of everything that has happened. If you are concerned about the safety of your child then you could speak to social services, but if you think he is safe then you have to just sit tight, follow your solicitor's advice and avoid any confrontation.
I know it is hard - we have helped a friend in a similar situation. Sadly some women have bad experiences with men and see them in a particular way. They expect all men to be as bad as those who have mistreated them in the past. If you are sure you have done nothign to deserve this treatment, it will seem very unfair, but make sure that you don't give your wife any opportunity to build anything against you. You can ask your solicitor to write to her and ask her to leave you alone if she is becoming a nuisance.
If she needs help, then I am sure that her family will find out soon enough that she is depressed.
Look after yourself and try and keep some stability and something good in other areas of your life - with your friends and work colleagues.
All the best
Liz