Does God have regrets? Does God cause us pain?

I have been reading 1 Samuel recently, and there are a few repeated verses whose meanings can't be what I think it is.
Here I took snippets with the particular verses bolded.
Basically I have two questions:
1. Why does it say "the Lord regretted"? does it mean that God feels he has made a mistake?
2. What does it mean by "the distressing spirit from the Lord troubled him"? does it mean something bad/evil can come from God, or that God would purposely give us evil spirit/thought?

If you happen to have read this part of the book before, or want to go read it now.. please share what you find out!

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

1 Samuel 15:
¹⁰ Now the word of the LORD came to Samuel, saying, ¹¹ “I greatly regret that I have set up Saul as king, for he has turned back from following Me, and has not performed My commandments.” And it grieved Samuel, and he cried out to the LORD all night.
³⁵ And Samuel went no more to see Saul until the day of his death. Nevertheless Samuel mourned for Saul, and the LORD regretted that He had made Saul king over Israel.

1 Samuel 16:
¹⁴ But the Spirit of the LORD departed from Saul, and a distressing spirit from the LORD troubled him. ¹⁵ And Saul’s servants said to him, “Surely, a distressing spirit from God is troubling you. ¹⁶ Let our master now command your servants, who are before you, to seek out a man who is a skillful player on the harp. And it shall be that he will play it with his hand when the distressing spirit from God is upon you, and you shall be well.”
²³ And so it was, whenever the spirit from God was upon Saul, that David would take a harp and play it with his hand. Then Saul would become refreshed and well, and the distressing spirit would depart from him.

1 Samuel 18:
⁹ So Saul eyed David from that day forward.
¹⁰ And it happened on the next day that the distressing spirit from God came upon Saul, and he prophesied inside the house. So David played music with his hand, as at other times; but there was a spear in Saul’s hand. ¹¹ And Saul cast the spear, for he said, “I will pin David to the wall!” But David escaped his presence twice.

1 Samuel 19:
⁹ Now the distressing spirit from the LORD came upon Saul as he sat in his house with his spear in his hand. And David was playing music with his hand. ¹⁰ Then Saul sought to pin David to the wall with the spear, but he slipped away from Saul’s presence; and he drove the spear into the wall. So David fled and escaped that night.