Is ending a harmful relationship, despite the friend's virtue, considered Islamically permissible and correct, and why does the feeling of regret and pain persist after this break?

The inquirer is correct in his statement that obeying the soul in what it desires of forbidden things leads to what is disliked, and compelling it to what it dislikes of acts of obedience leads to what it loves. He was right to cut ties with his friend, due to the major forbidden acts that relationship leads to.