I'm a single parent and my 9 yr old argues, back talks and never listens. I cry constantly, I need advice!?

I am a single mother of 3 great kids, a girl that's 5 and 2 boys that are 10 and almost 9. Their father left 4 years ago, signed his rights over and has nothing to do with them. My dad and stepmom help out some but I think my oldest is having behavioral issues from no male disciplinarian being present daily. My oldest gets in these moods where he never listens to me, constantly ignoring me. He argues with me, gets very defiant, and back talks everything I say. He is such a sweet and loving kid though, I just don't understand. I get so frustrated. I ask him to do something over and over and over before I raise my voice, then I have to yell before he'll quit ignoring me. But once I yet he yells back at me saying how horrible and mean I am. Tonight I officially felt like a horrible mother. He got in my face backtalking me and I slapped him. I didn't slap him hard but enough that it stung some. I couldn't believe it happened. I do not want to be that kind of parent but I don't know what to do anymore. I've considered counseling but it took a long time for him to get over his dad leaving and I'm worried bringing all that up will put him back to crying every day again. I even told him when I was crying one time that if he didn't shape up I was going to look into boys behavioral homes. I don't want to do that, I love him, and when he's not acting out he's the sweetest, most well behaved boy you've ever met, but it's a 50/50 thing and the acting out is usually when he doesn't get his way on anything, no matter how tiny...omg i'm rambling, i'm sorry, please, what do I do?