Is it permissible not to visit a neighbor because they were not invited to a wedding?

There is no blame upon you for not going to your neighbor on the occasion mentioned, unless he invited you to a wedding feast, in which case it is obligatory to accept the invitation, as long as the wedding does not involve anything forbidden. Islamic law enjoins good treatment of neighbors, for Gabriel enjoined the Prophet, peace and blessings be upon him, regarding neighbors to such an extent that he thought he would make them heirs. You should seek excuses for your neighbor and think well of him, and not respond to bad treatment with bad treatment, but rather with forgiveness and forbearance, for good character will weigh heavily in the scales on the Day of Resurrection.