CoStar Group’s chief financial officer is departing at the end of the month. Christian Lown is leaving July 31 to pursue an opportunity outside of the industry, the Arlington-based real estate data firm announced Monday. Robin Rossmann, who leads CoStar’s European operations, will take his place. The transition will occur just days after CoStar reports its second-quarter earnings on July 28. It also comes as CoStar faces pressure from investors over its spending on Homes.com, the Washington Business Journal reported.   CoStar’s stock was down 4% Tuesday morning. Lown served as CoStar’s CFO for two years and previously served as the CFO of Freddie Mac....