Is this normal?? Advice Please

Okay so please tell me I'm not crazy for thinking this is unusual. My current boyfriend(of two years, friends for over 5) has started talking to his ex-girlfriend, or well she has started to talk to him. They broke up like 4 years ago, and haven't talked really at all since. Their families are really good friends but Jon's family moved here from Maryland where she lives. The first time they had really seen each other since breaking up was last year when he went to maryland to visit some friends and she was home at the time. When jon came back he was mad because he thought that she was wearing the promise ring that he had gotten her, and knew if she was she was doing it to spite him. (note: I went with Jon when he bought the ring for the girl.) This past summer Jons family and her family and 2 other families went camping at a lake near my school so I tagged along. She didnt come for the first two days(coincidentally coinciding with the fact I could only come the first 2 days) and then she came, I decided I could stay the last two days. She seemed nice but immature and totally not Jon's type. She brought her FIANCEE with her so it eased my tension a little. I mean they did date for like 3 years, and its the only other person he has loved. I think the kicker is I knew him when they were dating so I have heard from him about how much he loved her and cared about her and I saw how heartbroken he was when they broke up. So its hard for me to be okay when them talking. Anyways so since camping she has been chatting him up. Facebook messaging and IMING, text messaging and calling, I mean not all the time but like once a week. This past week Jon was with me at school and she called, I just asked him to leave the room if he was going to talk to her. He came back like 5 minutes later. She had called him because she was on the way home from school driving and was bored so she called to chat. I mean if I were to call an ex boyfriend it would be because I was reminiscing or something, I don't randomly start having a friendship with x's that I havn't talked to in years. I try to be okay with it and tell Jon im fine if she calls him and they talk I just dont want him calling her. I mean she has a Fiancee, I wouldn't want girls calling Jon if we were engaged unless they really were just friends. This girl, I don't know, out of all of her friends WHY is she calling HIM. Please tell me there is something there and I'm not crazy. She like has this innocent flirt that you know isnt really flirting but it is, smiley faces in the text and tongue sticking out, like gah, she makes me think im crazy. I talked to Jon's mom about it and she said it was weird too. I tried to talk to him about it but I think he doesnt want to be mean because he doesnt want their mutual friends to be mad at him. I told him he can be friendly but NOT friends. Anyways any advice would be appreciated.