Dealing with a Long Distance Fiancé and His Ex-Partner

Does anyone have experience with having a long distance Fiancé who has a child they share with an ex partner? I have severe anxiety and depression and get in my head and get frustrated because I am not there physically. We’ve had a few run ins with his ex inviting him to celebrate holidays with their 6 year old son. I do not want to in any way keep him from spending time with his son, however, it seems his ex is always texting him and calling late at night talking about things unrelated to the care of their son. Recently, he did not tell me they had plans to celebrate the 4’th of July together until he was already on his way there. Last month he told me his son asked him to do something for Halloween with his mother as well. He hasn’t mentioned it again. So I had to ask him because I’d rather know ahead of time instead of the day of. He told me he’s going to spend Halloween with them because he wants to be there for his son. Am I being unreasonable to think they can celebrate separately? Or that he was going to go and not tell me anyways?