It's easy to say but I think you should try to stop panicing about it until he is back from holiday, until you speak to him you aren't going to get any answers so it's best not to keep going over things on your own, things can get blown out of proportion too easily like that.
When he returns from holiday just meet up with him as usual and ask him about still being on the site, try to say it casually rather than accusingly. He may be able to give you a satisfactory explaination or he may not, but either way you will be able to make a better decision after your talk than you will without seeing him.