Clara
Just declaring that it's possible it would be difficult, should I have had one.
I understand, of course; it's your time, as cousins, friends, who haven't had much time together yourselves. It was a bit on the insensitive side to do that, but I do think maybe you should try and force him to have fun, take his mind off her a bit while there with you. At least talk to him about it. You're brilliant at that.