So should a 16 year old in a serious relationship that's having problems end it for another guy?

Well I hate to break it to you hun but you can't change people. One summer won't change all his ways, maybe he's less of a jerk, but he won't turn into your perfect prince charming over such little time. If he's hurting you emotionally and you're not happy in the relationship, then end it, really what's the point of being with someone when they're constantly hurting you? I mean yeah fights and arguments do happen in relationships but when he's always being mean to you and can't trust you, then you have to really think if you want to stay with him. This other guy Danny seems like a better fit for you, but if you end up breaking up with Justin, don't just jump into a new relationship with Danny, get to know him better and take it slow before settling down again. Future and marriage at 16? Hun, that's way too early, and if he's already treating you like his property he's not going to be any different if you get married.