One of the new provisions of the new tax reform bill - background here - is that the long-standing tax deduction for alimony will no longer be available for separation agreements and divorces obtained after December 31, 2018. Specifically, the reform applies to "any divorce or separation instrument . . . executed after December 31, 2018" (emphasis added).
The new tax reform bill (https://www.congress.gov/bill/115th-congress/house-bill/1), which was signed into law on December 22, 2017, eliminates (http://money.cnn.com/2017/12/15/pf/taxes/alimony-tax-bill/index.html) the tax deduction for alimony payments for separation agreements and divorces obtained after December 31, 2018.