If you're legally separated or divorced before the green card is approved, USCIS will likely deny your case, because the basis of the petition (your marriage) no longer exists.

If you are just physically separated but still legally married, your petition may still be valid, but USCIS will closely review your case for signs of a genuine relationship.

 If divorce occurs after the I-130 is approved but before the green card is issued, your adjustment of status or immigrant visa will likely be denied.

If the I-130 has been approved and you're now in the U.S. with a conditional green card, you may need to file Form I-751 with a waiver if you later divorce.