Two: Don't do anything indecent in front of your roommate.

Three: Don't regard the dormitory as a hotbed of sexual intercourse.

As long as you don't do anything shameful, it's not a big deal to bring your heterosexual friends back to the dormitory.

In fact, there is no difference between good friends of the same sex or the opposite sex, but some people are too sensitive and think that what the opposite sex does is always shameful. Good friends are not hindered by the same sex or the opposite sex.