John Gill Commentary Psalms 35:14

"I behaved myself as though it had been my friend or my brother: I bowed down mourning, as one that bewaileth his mother." — Psalms 35:14 (ASV)

I behaved myself as though [he had been] my friend [or]
brother
Meaning either Saul or Doeg the Edomite, or some such evil man; somewhat like this he says of Ahithophel, (Psalms 41:9) (55:13) ; and Arama thinks he is meant here; as Christ of Judas, whom he called friend, when he came to betray him; and who not only ate with him at table of his bread, but was steward of his family, and carried the bag, (Matthew 26:50) (John 13:29) ;

I bowed down heavily, as one that mourneth [for his] mother ;
or as a mother that mourneth for her son, as Jarchi interprets it, whose affections are very strong; and thus Christ wept over Jerusalem, and had a tender concern for and sympathy with the Jews, his implacable enemies, and wept over them, and prayed for them, (Luke 19:41) (Matthew 23:37) (Luke 23:34) .