While I sympathize with you being the victim of gossip, I don't believe you have any case for defamation of character.
First of all, it does matter if what was said was true or not. If someone makes a true statement about you, (for instance that you are a child molestor) and you ARE a convicted child molestor, you could not sue for defamation of character, even if the whole world shunned you because of it. Statements made about you must be FALSE to constitute defamation of character (at least in Canada, where I live).
So, if what they said about you was that you are no longer a practicing JW, and that is true, then you have no case. Statements that you are spiritually weak, are subjective opinion and not provable either way, so again, you cannot make a case on those alone.
Also, you must know specifically what was said, and have witnesses willing to testify that they heard those things said about you. You then must prove that you were materially damaged in some way. Job loss, business damaged, illness from extreme emotional distress, etc.
It would be difficult for you to get pain and suffering for alienation of affection from your family and old friends, because, as you yourself admitted, you had already stopped associating with them even before words were said. It was you stopping associatingwith JW's that caused them to talk about you. So you cannot show that the gossip rifted any close relationships that were not already rifted. Even if you could, acquaintances at a KH are not close enough relationships that you would be considered damaged by the loss of them.
While I agree that JW gossipers are mean-spirited, you really have no legal case. I think you should move on. Living well is the best revenge.