It turns out to be his girlfriend when he tried to leave her for another woman. She couldn't handle him leaving her, so she shot and killed him. It all started when his wife had divorce him and took everything. He was homeless and penniless afterwards and then he had met a woman who took him in. She took care of him until he was back on his feet. He messed around, but she didn't mind as long as he didn't leave her. But he blew it when he made a lot of money on his job and was planning to leave her to settle down and marry another woman.

She's now in jail and I'm pretty sure she had regretted her decision.