A resident of a Weymouth sober home faces charges for a failed bank robbery in Roxbury on April 28 and a more successful one in Roslindale 90 minutes later - in which he and an accomplice allegedly threatened to shoot bank employees who didn't turn over some cash, pronto. Steven Harris, 34, was arrested Sunday outside the Weymouth sober home, on one charge of bank robbery by force or intimidation and one charge of aiding and abetting a crime, according to federal court records unsealed today. The records do not name his alleged accomplice, which means he may still be on the lam. Harris and his pal showed up at the Santander Bank branch at 2189 Washington St. in Roxbury - after first meeting up outside a nearby YMCA and driving over - around 10:10 a.m., according to an affidavit by an FBI agent on the case: Upon entering the bank, Subject-1 [the unnamed suspect] brandished a black-and-tan-colored firearm, which he pointed at bank staff, demanding money.…