Advice needed!!

My husband and I have been together for 2 years now. He was married for 2 years and divorced for 5 before we met. Last Christmas I spent it with him and his family (we live in Finland but I'm from Mexico) so it was very some dual for me. His ex-wife send him a message on FB wishing him and his family happy holidays and I was ok and glad that they are in good terms ..... until they kept talking for 3 more hrs. I told him I wasn't to happy with it and it passed. She send him a happy birthday and that was it for a hole year. And today he sent her a message and have been talking most of the day. I don't know if being annoyed/angry is reasonable or is just me being crazy.

He know ok with them sending an occasional message (not 3 hrs long conversation) being polite . They share history and I'm glad they didn't end up hating each other but I don't know if telling him I don't want him talking to her that much will be taken as me overreacting.