I have to say that if I were a mother, I would be mad too. I don't think it was an accident either. I don't think there is a such thing as an accidental hicky. You have to put yourself in his mother's shoes. I know this is from experience. My boyfriend left a couple hickies on my neck. My father saw and had a talk with my boyfriend about it. He wasn't mean or anything. He was just concerned, because those hickies looked like I was someone I was not. In other words, I guess my dad didn't want me looking like someone who "got around."
14 is a very young age. You are going to go through quite a few boyfriends before you find the right one. Don't rush yourself and don't be so quick to give your heart and body away.
Also, parental support is a must. I don't think I would be comfortable dating a boy who my parents didn't approve of.
I think you should tell your mom about the hicky. Not to beat your boyfriend's mother to the punch, but because you want your mom to know. Parents like it when you talk to them about things. Trust me. It will make your relationship with your boyfriend better as well as your relationship with your parents.
Good luck!
~Jessica
