my boyfriend was playing around and being childish and hit me

Rose
Sorry it's long, it's a long story. So just some background info, I'm 17, my bf's 18 and in college but home for the holidays. We've been together 7, almost 8 months now. I slept over my his place because the weather was terrible and icy and I'm already a bad driver and live an hour away, so I truly didn't know if I could make it home safely.
Anyway, we were playing around after having just had sex around 2.30am. So we're talking, and suddenly he slaps me, not hard, but I got startled. It kinda felt like betrayal because the touch that I'm so familiar with that is related to love and tenderness hurt me. He also laughed afterwards, but I made it a bigger thing than it was. He was just playing around and being stupid, he just wanted to see if I like being slapped in bed, he thought it was funny because it was so stupid, which I understand. As soon as he did it and saw the fear in my eyes he felt awful. And I know him, if he ever hurt someone he cares about, he wouldn't know what to do with himself, he's struggled with depression from emotional abuse growing up. So anyway, I got quiet, and he kept comforting me saying things like "I'm so sorry, Rose. I don't know why I did that, that was so stupid of me. I would never do anything to hurt you. I would never use my strength against you, never." He would brush his thumb against my cheek and I would close my eyes for a second, kind of a flinch I guess and he said "and now you're scared of my touch. And you're scared of me. Oh my god, what have I done...." As soon as I really realized what was happening I told him I'm fine, I accept his apology, it only startled me, I wasn't afraid of him. He startles me all the time when he jumps out at me from behind doors, but this time I just wasn't prepared for it. I told him I'm fine, I'm not hurt and that nothing has changed, and I love him. He said okay, and we snuggled, and I put my head on his chest for a little bit. But when I looked up I saw tears streaming down his face, and I said "oh, baby. I'm alright, look at me, I'm fine. You're fine. We are and will be fine. I promise, I wouldn't leave you over something so stupid and silly, I know you were just horsing around." And he nodded and I put my head back. I waited a little to look up and again, and I saw he was still crying. I asked him why and he said "because I'm worried you don't love me anymore and that you'll leave me" which is one of his biggest fears, and it is also one of mine. I told him, "I know it didn't come out of anger, you was just being stupid, that's all. But, God forbid you do it out of anger, I will not be staying." Which scared him but he understood. He was still so sad, and crying and worried, but his eyes were closed now, and I said "awh, baby. I'm sorry" and I went to brush my thumb along his face but he pushed my hand away as soon as it touched, without opening his eyes and kinda growled "don't you dare apologize, none of this is your fault." 
He's a very sensitive guy and is very in touch with his emotions. I know he didn't mean to hurt me (and honestly he didn't hurt me, I was just dramatic), He just likes to be dominant. None of this happened out of anger. And I still love him with all my heart and wouldn't never leave him for something as stupid and silly as this.
I just wanted to share my story.