That is conditional GC you will recieve. And after 21 months of valid marriage, again you need to apply for independent GC - in which you need to provide valid proofs e.g. shared bank accounts, etc etc. Then you will get independent GC.

In this mean time, if your marriage fails before 2 years, there is high chance of you loosing GC. However, if you can prove that the marriage was geniune one but did not work, you are still able to get GC. Go to state department web, download pdfs, fill it in, and send along with required fee.