I am enjoying the lively discussion in this thread.
In my mind there is absolutely no doubt that Bingley is both responsible and culpable, though I would not go so far as dishonourable.
A man is always responsible for his own actions. Sometimes one is forced to do something due to some irresistible outside pressure or circumstances. Darcy’s “assurances” certainly does not qualify. If Darcy was his guardian who held the purse strings it would have been different.
And the assessment of Bingley’s character, whether he is wishy-washy, malleable or amiable or whatever is irrelevant to the point that he is responsible for his own actions in distancing himself from Jane and therefore culpable.