STAMFORD — A West Side man was charged with stabbing his girlfriend in the arm with a knife late Wednesday night. Police responded to a Fairfield Avenue apartment about 11 p.m. Wednesday for the report of a stabbing and found Wilmer Cardona-Sandoval, 28, sitting on the porch. Cardona-Sandoval’s girlfriend told police he came home drunk, threw her on the bed, got on top of her and demanded his half of the rent back, the report said. The woman said he then pulled out a knife and tossed it from hand to hand, police said.