hi, Dan
i had thought about your problem and there are my advices:
maybe, you should talk to Jonathan. You should help hm to solve his problems like real friend. maybe he does not understand that something is wrong
You can tell his parents that his behavior has changed.
but do not impose, otherwise you certainly do not make peace
(надеюсь, там все правильно, за 100% грамматику не ручаюсь)
I think that Jonathan needs some time to understand that he has bad friends. You can send a message, and speed up the process. One more thing, remember, have you quarreled for some time? If you quarrel, make your first move, and renew your friendship with Jonathan.
