How do YOU think Peter would react to coming home to find someone else making Elias Lonely?
Sorry for not answering earlier anyways.
Hm realistically? Probably smug at first, a sort of: look how low you have fallen to get so lonely.
Afterwards, if it continues and Elias gets worse, he may start to get annoyed and be bothered by it. Simply because that sort of thing is their deal. Peter could objectively feed from it, but it would be grinding on his nerves.
Someone else other than him got to Elias and is making his life miserable. That won’t stand.
So after his smugness and then the realization that he is not actively enjoying this like he wants, he may get angry and sort it out.
This man does leave the job of killing others if it’s not with the lonely to others, and he has threatened Elias, but they have their own way or game to play it with. So by then, he would try to snap Elias out of it, do some cleaning up about the avatar, and then once Elias is fine, be smug again.
He is not going to want to admit he was worried. So teasing and being smug till Elias kicks him out for a bit, but not for long anyways. Peter did do him a favor and he will milk out the fact that he took the effort to make him less lonely to mess with him as well.
Loop of them both bullying the other while simultaneously actually having feelings about the other they don’t want to deal with.
They probably make out and go feed on someone else’s misery to wash it out before just being maybe a tad softer with the other after the whole ordeal. Elias may offer a name for Peter to sacrifice and Peter may get something nice for Elias.
(If they make our on the couch and then fall asleep there, that’s just me wanting them to be happy a bit)
Anyways I hope this answers your question. I love getting to talk lonelyeyes.