@ManyToMany remove relation in Spring

    @Override
    public void deleteGroupById(Group group, User user) {
        user.getGroupSet().remove(group);
    }

@ManyToMany(mappedBy = "group_list")
    private Set<User> userList = new HashSet<>();

@ManyToMany(cascade = { CascadeType.ALL })
    @JoinTable(
            name = "user_group",
            joinColumns = { @JoinColumn(name = "user_id") },
            inverseJoinColumns = { @JoinColumn(name = "group_id") }
    )
    private Set<Group> group_list = new HashSet<>();

 group.getUserList().remove(user)

public interface UserGroupRepository extends CrudRepository<UserGroup, Long> {
}
...
public interface UserGroupService {
  deleteRelation(long userId, long groupId);
}

...
    @Override
    public void deleteRelation(long userId, long groupId) {
        Set<UserGroup> userGroupSet = new HashSet<>();
        userGroupRepository.findAll().iterator().forEachRemaining(userGroupSet::add);
        for(UserGroup ug : userGroupSet)
            if(uq.getUserId()==userId && uq.getGroupId() == groupId)
               userGroupRepository.deleteById(uq.getId());
        userGroupRepository.deleteById(id);
    }

//imports ...
@Entity
public class Group {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @Column(columnDefinition="DATETIME")
    @Temporal(TemporalType.TIMESTAMP)
    private Date lolA
    @Column(columnDefinition="DATETIME")
    @Temporal(TemporalType.TIMESTAMP)
    private Date lolB
    private int lolC

    @ManyToMany(mappedBy = "group_list")
    private Set<User> userList = new HashSet<>();

   //geters and setters ...
}

//imports

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    private String name;
    @DateTimeFormat(pattern = "yyyy-MM-dd")
    private Date birth_date;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(
            name = "group_user",
            joinColumns = { @JoinColumn(name = "user_id") },
            inverseJoinColumns = { @JoinColumn(name = "group_id") }
    )
    private Set<Group> groupList = new HashSet<>();

//geters and setters
}

public interface UserRepository extends CrudRepository<User, Long> {
}
...

public interface GroupRepository extends CrudRepository<Group, Long> {
}

public interface UserService {
    Set<User> getAll();
    User findById(Long id);
    void deleteById(Long id);
    void update(User t);
    void deleteGroupById(User user, Group group);
}

@Service
public class UserServiceImpl implements UserService {
    private final UserRepository userRepository;

    public UserServiceImpl(UserRepository userRepository){
        this.userRepository = userRepository;
    }

    @Override
    public Set<User> getAll() {
        Set<User> userSet = new HashSet<>();
        userRepository.findAll().iterator().forEachRemaining(userSet::add);
        return userSet;
    }

    //findById wyciąłem tą metodę bo działa dobrze

    @Override
    public void deleteById(Long id) {
        userRepository.deleteById(id);
    }

    @Override
    public void update(User t) {
        userRepository.save(t);
    }

    @Override
    public void deleteGroupById(User user, Group group) {
        user.getGroupList().remove(group);
        group.getUserList().remove(user);
    }
}