He Talked To His EX About Me!

My current boyfriend and I have been having some issues. He recently went on a trip to his hometown to visit his family. The night he came home his cell phone rang at 3 am. The next day I asked him who called him so late. He admitted that it was his ex-fiancee and that he'd been talking to her while he was away. She lives in far away, in a different state, so he didn't see her on his trip but used the opportunity to talk to her without me around. He also admitted to talking to her about OUR problems and flirting with her, too. My reaction was sadness, disappointment and a little jealousy.