Spring Data JPA, change to one attribute of Many To Many entity is wrongly being shown on all other entities that share it - spring

Question

When I make changes to one attribute of an entity, it also somehow gets changed for every other entity that uses that entity. I have three entities as you can see below.
Students and courses need to have a many-to-many relationship between them and the course needs to have a one-to-many relationship with course lectures.
When I make changes to courses or course lectures that belong to a specific student by doing #Transactional student.getCourse().get(0).setTitle("whatever"), those changes are also reflected in other students who share the same course. I need help with this, thank you
The student class
public class Student {
#Id
#SequenceGenerator(
name = "student_sequence",
sequenceName = "student_sequence",
allocationSize=1
)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "student_sequence")
private Long studentId;
private String fullName;
#Column(name = "email_address", nullable = false)
private String email;
private String username;
private String password;
#ManyToMany(mappedBy = "students", fetch = FetchType.EAGER)
private List<Course> courses ;
public void addCourse(Course course) {
if (courses == null) {
courses = new ArrayList<>();
}
courses.add(course);
}
Course Class
public class Course {
#Id
#SequenceGenerator(
name = "course_sequence",
sequenceName = "course_sequence",
allocationSize = 1
)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "course_sequence")
private Long courseId;
private String title;
private double courseRating = 0;
private LocalDateTime createdAt = LocalDateTime.now();
private double completedProgress = 0;
#Embedded
private CourseInformation courseInformation;
#OneToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER)
#JoinColumn(name = "course_id", referencedColumnName = "courseId")
private List<CourseLecture> courseLectures;
#ManyToMany(
cascade = CascadeType.MERGE,
fetch = FetchType.LAZY
)
#JoinTable(
name = "student_course_mapping",
joinColumns = #JoinColumn(
name = "course_id",
referencedColumnName = "courseId"
),
inverseJoinColumns = #JoinColumn(
name = "student_id",
referencedColumnName = "studentId"
)
)
#ToString.Exclude
private List<Student> students;
There is no relationship mapping in the CourseLecture class.

Answer 1

This is not wrong, but just the way JPA works.
Technically it works, because they all reference the same instance as JPA guarantees to always return the same instance for a given class and id in single session.
If you don't want that you'd have to do the work either in different sessions, or you have to change your data model, so that each student has their own course. Of course this would be a strange model.
Update based on your comment:
Looks like indeed you need a different model, instead of Student -N-M-> Course you need something like Student -1-N-> Attendance -N-1-> Course, making the mapping table of your relationship into an entity and allowing it to store extra data that is specific to Student AND Course