Kinda worried, my boyfriend is REALLYY close to his ex?

You should ask him. And then you should ask her. I know it sounds weird but see what he says. He might say that they are just friends, but when you talk to her she might say that he is flirting big time. I'm sorry if this isn't what you wanted to hear right now, but for some reason, most people never seem to stop loving their first loves. Jake and Mary might have been friends before that, so he might just want to stay friends with her. And for the whole kissing thing, ask her about that also, she might tell you what you need to know. Whatever happens, I hope that everything will work out for the best. I really hope that this has helped, good luck!!!