A Massachusetts man brought his girlfriend to the New England Aquarium in Boston, where he arranged for divers in a fish tank to hold a sign proposing marriage. “Will you marry me, Katie?” the sign read. Groom-to-be Peter Gallagher, 29, brought his girlfriend Katie Ellis, 28, to the aquarium Saturday afternoon for the prearranged event. “I’ve been nervous for the past week. Very nervous,” said Gallagher, who is a middle school teacher in Lakeville. “But I wouldn’t have done this if I was afraid she’d say no.” Ellis, a fellow teacher, said yes. The couple have only been dating since December, but have known each other since they were teenagers, Gallagher said.