Right. I'm still not clear so I will provide very general advice.
If you are Italian then you are an EEA national. As a non-eea national he would have to apply to for a residence card based on your marriage in order to stay here. he would have to apply using form EEA2. If he has made this application or has received his residence card and you are no either no longer married or living and having a relationship as man and wife then you can inform the UKBA.
They will take the decision to curtail his residence card if you are divorced (ie. you have received your decree absolute in your divorce) and will ask him to leave the country. If they do and he does not leave then he will become an overstayer again and if they catch up with him they may deport him.
If you have been married for a period of three years then he will retain his right of residence upon divorce, meaning that will be able to stay in the UK.
If they have not made a decison on an application that you have recently submitted then they will simply withdraw the application and he will remain an overstayer.
This may not be great news for you if you wish to divorce him because you will need to know where he is in order to file a petition for divorce in this Country (if you are married).
If you wish to inform the UKBA (and you are probably under a duty to do so) then you should write to the UKBA giving full details of you, your husband, his application for a residence care based on your marriage and state that you are no longer living as man and wife and that you will petition for divorce (if in fact you are).
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