I married a foreigner on a student visa, in California. Once we got married he applied and received his temporary residency and now is in the process of receiving his permanent residency. Our relationship coincidentally ended once his paperwork was in process and he is seeing other people and has since left the marriage. Am I eligible to file for annulment?
Can I contact Homeland Security and report his actions? It is very clear he entered this marriage fraudulently.

Ok, you are hurt, yep you can report him to ICE, don't expect them to do anything, about 100,000 aliens per agent to try and do something about
They may address it in his final process review. And that is still maybe.
Since many marriages end in divorce anyway, he can just claim it did not work out.

So move on, it happens, most likely you will need to file for a divorce.

Anullment of a marriage usually only happens if the marriage is under 6 months. Longer then that you will have to file official paperwork for separation and disolution.
California Courts
Try that link it may help you and also further answer your questions. Its for the California court system. It's a pretty good reference link.

My husband hid his impotency status before we were married 2 years ago. Am I eligible to get this marrige annulled?

My husband hid his impotency status before we were married 2 years ago. Am I eligible to get this marrige annulled?

No, not on those grounds. You need to file for divorce.