My (19F) friend (19M) cancelled our plan to do a sleepover at my house at the last moment. Because his cousins were visiting him this last week, and he said that he wanted to spent the weekend with them. For context, we planned this weeks ago, he was really excited about it. My dog just died three days ago, so I was pretty upset, my other friend also was mad about the situation, cause early in the day he joked about not going to the sleepover, but he decided to cancel at the last minute. He had all the week to be with his cousins, and also I haven't seen him in months because over the summer he went to the US to work. It seems to us that he has been weird in everything. He has been drinking a lot, going to party in the middle of the week, at uni he is just taking three classes. We are worried for him, we think he is being immature. What is the right way to approach this? I haven't reply to his messages.

English is not my first language, so bear with me.