Here is an example of the longer parts of dialogue in my story with the real names omitted: “I don’t feel right with what just happened Smithy” Susan said, choosing her words carefully as to not upset him, “They deserve to know the total truth about what’s really going on behind closed doors. They will feel deceived and find us permanently untrustworthy if we don't tell them right now.” Is this too long for a piece of dialogue?
I don't think it's too long, but it's a little stilted and unnatural sounding. Try saying your dialogue out loud to see whether it rolls off the tongue easily. You can use phrases like 'they will feel deceived and find us permanently untrustworthy' in narrative but they just don't sound like something someone would say out loud.
It does come across as a bit wordy, in that you can say the same thing, and strike an almost stronger impact, by omitting some of the words. "I don't feel right about what happened." "They deserve to know the truth about what's going on behind closed doors." "They will feel deceived and find us untrustworthy if we don't tell them now." I understand the need to convey the urgency of a situation, and put a strong emphasis on the scenario. I tend to do that, also. It always leads to me having to do a lot of rewriting in the end because it just doesn't flow very well.
while it does sound sorta stiff/stilted, the real problem here is not how much she's saying, but that comma after the dialog tag, since what follows is not the continuation of a sentence, but a new one... you're also missing a needed comma before the dialog tag...
