Jesse Mermell is stepping down from the Board of Selectmen on Monday to become the communications director for Governor Deval Patrick. Mermell, 32, has served as a selectwoman for almost six years, and is leaving with about four months left on her term . “I will miss the board terribly, but look forward to continuing to be engaged in the civic life of our wonderful community, and to further serving Brookline in my new capacity,” she said last week. Mermell will also be leaving her job as the director of the Massachusetts Association for the Blind and Visually Impaired. In a discussion about how the board should deal with the open seat, Town Administrator Melvin Kleckner said Tuesday that a special election would cost about $60,000, and couldn’t be held any sooner than April, or roughly a month before the town’s annual election. Chairwoman Betsy DeWitt has said given the timing, it might make more sense for the Board of Selectmen to operate with only four members until May. The board will revisit the issue during its 7 p.m. meeting Tuesday in Town Hall.