Oh no
I hope it wasn't me - I tease him too much.
I don't think anyone's responsible, at least not anyone specific.
If anything, the general moment might have been the camel back-breaking straw. I haven't been here long enough to know for sure, but it does seem to me that on occasion there are moments of high tension where one person or another may feel ostracized, and maybe having enough of those (especially directed at oneself) would lead a person to decide they needed to take a break from the whole experience for a bit.
In any case, I can't imagine feeling personally bad about it is going to help anyone (or bring Beren back before he wants to return). This is, after all, a public discussion. If he is curious, he can see plainly that no one meant harm and that we regret his departure. Protracting it further is probably not worth anyone's while.