Ex-girlfriend is jealous of me joinging Latin America singles club

My ex-girlfriend and I stayed friends months after our break up. I know some people would really raise eyebrows on this arrangement but thats what we agreed on. We talk from time to time but its mostly about neutral stuff, nothing about us anymore. Last week she messaged me asking if its true that I joined this Latin America singles club thing. She said a friend told her about it but wouldnt drop a name. I noticed that she was acting all jealous about it. Although she said that she was happy for me, I could see in her messages that she was actually feeling something negative about it. Trust me, Ive mastered reading her emotions behind her messages. How should I react about this?