Radak #1: I should not be like something despised. Rather, turn to me with mercy and love.

Radak #2: Also this refers to Ru'ach ha'Kodesh (mentioned later in the verse). The verse repeats itself. David had Ru'ach ha'Kodesh - "Ru'ach Hashem Diber Bi u'Milaso Al Leshoni" (Shmuel II, 23:2). He said the Mizmorim with that Ru'ach. Now that he sinned, it departed. David prayed that Hashem never take it from him. Even though now it was taken, Hashem should return it.

Sha'arei Teshuvah (1:42): Hashem should desire me like before the sin.

Malbim: After Hashem will create a new heart for him, he should not return to his folly, and not veer from clinging to Hashem. There are two aspects to clinging. (a) The person is by Hashem. (b) Hashem is by the person, for the Tzadik is by Hashem and tied in His knowledge, there is Hashgachah over him from all mishaps of time. He is not under nature, rather, under Hashgachah.

Rashi: Ru'ach ha'Kodesh should not be far from me. Malbim - this is what guides a person towards attaining Emes and perfection of his Nefesh.

Sha'arei Teshuvah: Refer to 51:14:1:2.