Suing for defamation means you have lost specified amounts of money due to false statements made about you, or you have been falsely accused of a crime in which case you may recover "nominal" damages without proof of actual monetary losses.
If it is an HOA matter, then if this person has falsely told the HOA you are violating the rules or bylaws, then you should have had the right to contest any action by the HOA, such as any fine they dealt out to you. Or even if they warned you about these allegations, then you would have had the right I am sure to submit a written reply so your "standing" would not be affected.
Since you provide no detail of the kinds of things this person is saying, then there is no way of determing whether this person has committed defamtion against you. You would not receive any award in small claims or any other court without providing detail as to what the accuser is saying about you, to whom, and how it actually caused you any harm.
False allegations to your neighbors would not go to the HOA unless they report something directly to the HOA, and the HOA makes a record that could be used against you as past history in the event of future alleged violations or if the HOA brings an action against your based on violation of HOA bylaws.
You also have provided no information as to how your "vested interest" in the HOA
is impacted. Detail would need to be provided to any lawyer expected to give you information or to any court expected to provide you any sort of remedy.
Talk with the friends and neighbors the false accuser has talked with, and straighten them out with a brief explanation of the truth. They may tell you they do not believe the other person anyway, in which case you have not been damaged. Do not prolong this, either they will accept what you have to say or not. In any type of claim, you have the duty to "mitigate damages" so you cannot just sit there and let false allegation be made, so protect yourself with the truth. On the other hand, don't take part in an ongoing "feud" as no judge will be interested in that.
If you straighen out the people to whom these alllegations have been made, with the truth from you, and the accuser persists then you made need to take action. If the person is maliciously continuing to cause you harm, you could file an "anti-harassment" petition but it would have to be speech by them that is clearly not protected by the First Amendment. Any doubt, and you would not get a restraining order.
Anything you can do to simply ignore this person would be the wiser route. Better to go around a tree than through it. If they are emailing you still, then block their email.
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