You may still qualify for a green card through a process called “widow(er) petition”, even after your spouse dies.

If you were married for at least 2 years at the time of death, and not legally separated, you can file Form I-360 as a widow(er).

If you already had an I-130 pending, it may be automatically converted to an I-360 (in some cases), but you should still follow up with USCIS.