Should exes talk to each other?

I want to know what people think. My husbands ex girlfriend (and first sex partner) contacted him via facebook about three weeks ago. They dated when they were teenagers, about 14 years ago. She is married with 2 children. The conversation started out innocently enough, but then progressed to her wanting to meet him for coffee. He pointed out to her that we live 3000 kms away from her, so she asked if she could call him on the phone some day. He told her that I wouldn't like it, but gave her the number anyway. Then, he erased the emails from his facebook account without telling me. I found out because he got a text message from her stating "Did your wife find out, so we can't talk?" This sent me over the edge, and when I tried to call her and talk to her, she hung up in my ear. He says he didn't tell me because he knew I would overreact (I can tend to do that, I admit it), but I still think that he should have respected my feelings and told her no when she asked for his number. I'm not actually mad about them talking to each other, I'm made about the sneakiness between them both. I wonder what her motives are, married with two young children. My husband acts like it's no big deal, and I'm pissed.