“been with you.” In this context the phrase is a euphemism for sex.
“For now, my sister, be quiet.” Absalom pretends to care for his sister, but in reality he is using her as part of his plan to gain the throne. Amnon’s rape of Tamar will give Absalom, David’s third son, a chance at removing Amnon, David’s first son and apparent heir to the throne. David’s household was riddled with evil.
“Do not take this thing to heart.” This statement was “heartless” on Abaslom’s part. What was Tamar supposed to do?
“desolate.” The Hebrew word occurs almost 100 times in the Hebrew Old Testament and most often refer to land that is not farmed and is barren (cp. its first use, Gen. 47:19). Thus, when used of a woman it refers to her being unmarried and therefore without children. It occurs in Isaiah 54:1, where it is used of the northern country of Israel which has been carried away into exile by the Assyrians and is compared to a “desolate woman.” The prophecy in Isaiah that the desolate woman will have more children than the woman with a husband is a prophesy of the fruitfulness of Israel in every way in the future Millennial Kingdom. Tamar was unmarried, without children, and mostly isolated from others. The joy in her life was gone, and almost any contact with the family of David would have only reminded her of the crime of her half-brother Amnon who was the crown prince and likely heir to the throne of David. The Bible does not say if Tamar remained unmarried in her brother’s house for the rest of her life, we just don’t know because the record of Tamar ends here and we hear nothing more about her. Her brother Absalom died in his rebellion against David, and certainly after that she likely would have had to move. She stayed in Absalom’s house for an unstated amount of time; it is possible that she even married and moved on with her life.