It's an issue you need to be aware of and one that probably you would best be served by consulting an attorney. What happens is, after you have a conditional green card issued, the government is going to want to see that you have maintained that bonafide marriage, and they can make the assumption that, if you're separated or divorced, your intent at the time of getting the original green card was only to get the benefit of a green card, not to enter into a legal marriage. The bottom line is you now have a higher burden of proof, and you have to, through some quality evidence, convince the government that the marriage at the time you entered into it was legitimate, all of the right romantic reasons, and not just to get that green card. It's important that it be handled very, very well.