1 Kings 1:1 When King David was very old, he could not keep warm even when they put covers over him. 2 So his attendants said to him, “Let us look for a young virgin to serve the king and take care of him. She can lie beside him so that our lord the king may keep warm.”

3 Then they searched throughout Israel for a beautiful young woman and found Abishag, a Shunammite, and brought her to the king. 4 The woman was very beautiful; she took care of the king and waited on him, but the king had no sexual relations with her.

This is from the blueletterbible.org site.

King David was old, advanced in years: This was the twilight of a glorious reign. David was now so old that he could not even keep himself warm, much less rule the nation.

Let her lie in your bosom, that our LORD the king may be warm: This sounds strange-perhaps even immoral - to us, but this was proper of David to allow. This did not bring a moral cloud over the last days of David's life.

It was proper because it was a recognized medical treatment in the ancient world, mentioned by the ancient Greek doctor Galen. When Josephus described this in his Antiquities of the Jews, he said that this was a medical treatment and he calls the servants of 1 Kings 1:2 "physicians."

It was proper because David almost certainly made this young woman his concubine. While it was unwise for David to take more than one wife, it was not at that time illegal or specifically prohibited by God. Later, Adonijah would condemn himself to death by asking for Abishag as a wife. His request would only be so outrageous if Abishag had belonged to David as a concubine.

Abishag the Shunammite: From ancient times, many have wanted to associate this beautiful young woman with the Shulamite addressed in the Song of Solomon (Song of Solomon 6:13 and throughout).

"According to the theory, as she ministered to David, she became romantically involved with his son Solomon and was later the subject of his love poem." (Dilday)

Yet we must say that this conjecture at best - and Shumen is not the same as Shulam. "Shunem, the modern Solem, lay eleven kilometers south-east of Nazareth and five kilometers north of Jezreel in Issachar territory, and was visited by Elijah (2 Kings 4:8). There is no need to identify Abishag with the Shulammite of Song of Solomon 6:13." (Wiseman)

She cared for the king: This scene of David's diminished ability shows that question of David's successor had to be addressed. King David could not last much longer, and his family history had been marked by treachery and murder. At this point, it was worth wondering if there could be a bloodless transition from David to the next king.

So the question is... did David.... who had taken on Goliath in his youth... is reported to have had hundreds of women in his lifetime.... went from shepherd boy to king of Judah and then Israel.... have relations with that woman.

Another question is... after hundreds of women... why does it matter???? We heard about a few of David's women. They all had a story... Mical was won at war, given to someone else and returned.... Abigail was a bully's wife who saved David from having to kill her bully husband.... and Bathsheba was a soldier's wife that David had an affair with.... it resulted in the murder of her husband and the death of a baby boy.

This woman doesn't have a past. Her father wasn't king, she didn't have a husband... but apparently she has a future. Apparently her future has something to do with David's son, Solomon. If that's the case.... I doubt seriously that David had a sexual relationship with this woman.