Huddled in an underground shelter in war-battered eastern Ukraine, Oleksander and Lyudmila Murenets spend more time together these days than at any other point in their four decades of marriage. The tension is starting to show. Theirs is far from the only marriage in eastern Ukraine buckling under the stresses of wartime. Throughout the Donbas region, the combination of fighting and freezing temperatures is forcing couples to spend long periods in close quarters, straining some relationships and strengthening others.