In Hashem's great mercy we are zoche to know that Dovid HaMelech actually had a man KILLED in order to be with that man's wife. And yet he went on to do teshuva and to write INCREDIBLE Tehillim of PRAISE to Hashem, to receive nevua from Hashem, and his son built the Beis ha'Mikdosh, and it will still be his seed which will bring geulah to all of humanity. Basically the point is, he remained an incredible Eved Hashem and he did not ever let his sins deter him from going on being that.
Let us remember this lesson, that one can even approach a sin which is un-fixable(which is to say, to precipitate DEATH of another human) and still do teshuva and still be an Eved Hashem. In the text of Tehillim, we see that it is because of Dovid HaMelech's spiritual greatness of attributing all praise always to Hashem, that this was possible for him. He did not trust in his own abilities to get him out of situations AT ALL. (See Chizuk e-mail #982 on this page for more on this idea and Dovid Hamelech's fall). This has given me personally a great chizuk in all of my personal failings, to keep on trying to improve and not to feel bad praising Hashem even when I am personally in a very low state.