So is everybody from Bel's party like this? Unable to help their friend or even come to terms that they can't do anything (or at least think that they can't) for him, so went with what they did know and hoped that would lead to a solution?
I was rereading this series when the new chapter dropped and it seemed like he cut-off any communication from them after he left the party to not slow them down. So its possible that he didn't even say good-bye which did not do them any favors.
Probably, yeah. He is at a fault too. He did suffer mentally, but he didn't let it show to his friends. So he suffer alone, while his friends can only worry about him. At first he stopped doing quest with them, since he's cripple now and going with easy chore quest alone(like gathering herbs). But then, one day all of a sudden he just went missing. They blamed themselves for not being able to do anything for him.
The party break apart not long after, since according to some adventurers they have heard rumors of them in a party together, but don't know if it was actually true. The mage guy looking for power in grief, becoming a high ranking and renowned. The sword guy also became high ranking and renowned, but both of them went missing at some point. Some people have heard of the elf girl, but she went missing much earlier and nothing much known about her.