The question is not clear.

If you don’t pray the Sunnah prayers, you are not sinful but you shouldn’t allow Satan to fool you into not praying it because you feel more Khusho’oa. You should know that praying the Sunnah would increase your Iman and it wouldn’t reduce it.

When I sometimes miss a prayer or I sin, I feel so depressed, when I pray the Fardh I enjoy more then when I pray 2 rakaa’at before fajr