I believe you are referring to the I-864 Affidavit of Support. The I-864 is a contract between a sponsor and USCIS that an intending immigrant will not apply for and receive "means tested public benefits (i.e. TANF, food stamps, rental assistance, etc.). If your sponsor had filed an I-864 for his now ex-wife, he may have to include her in calculating the household size. The household size impacts how much a person must earn to prove that he can be a sponsor. The income requirement can be found at http://www.uscis.gov/files/form/i-864p.pdf. Additionally, the I-864 may still be in effect if his ex-wife is still a permanent resident and has been one for less than 10 years. However, whether the I-864 is still in effect does not mean that this proposed sponsor can not be a sponsor for you now.