Do NOT sign those immigration papers or you can be subject to prosecution for marriage fraud - up to 10 years in prison (typically 5), plus $250,000 fine. Notify ICE that your foreign spouse has filed a divorce petition against you & is blackmailing you to sign his papers for release of conditions.
The marriage is over & he is the one who filed. There is NO way you can legally sign the papers for removal of his conditions since this marriage is dead and done with. You would be legally liable for his support if you enabled him to remain. And yes, he could remarry & bring in his foreign gf as soon as the divorce is final, while you are still on the hook for his support!
Actually, you are being blackmailed, a felony. He is making demands while threatening you. Report this to ICE as well as filing a police report. Get him deported or your life ain't worth a bean.
Your best bet is to get an attorney immediately, file for an annulment based upon his defrauding you for immigration benefits, file the police report of blackmail, and report it all to ICE: the breakdown of the marriage, you now understand that he only married you to obtain immigration benes, he is blackmailing you to obtain immigration benes he is not entitled to, and therefore you have filed a petition to annul this marriage, and hereby revoke the Affidavit of Support since you were induced to sign it by his defrauding you.