Is it possible that my Green card can be revoked because of fake signature on the gren card lottery application?

Details:

I won a green card lottery in 2004 and moved to US where I presently reside.

The problem is that when I submite an application for green card I did NOT sign it. I did not know the rules because I did not speak English. My friend did it for me (US citizen). Now we broke up and he is threatening me that he will provide this information to USCIS.

Am I going to run into serious problem after he commits that action? Can my Green Card be revoked or something? What is my chances to win this case (I mean in court) if they will conduct legal signature analize / expertise?

Thanks.