Piyush behaves strangely at times and, therefore, nobody gets ...... with him.

Piyush behaves strangely at times and, therefore, nobody gets along with him.
In this context, "gets along with" means to have a harmonious or friendly relationship with someone. The phrase indicates that because of Piyush's strange behavior, others find it difficult to establish a rapport or bond with him. Therefore, "along" is the most appropriate choice to complete the sentence, conveying the idea that nobody can develop a smooth relationship with Piyush due to his peculiar actions.