I'm not comfortable with my long distance girlfriend hanging out 1 on 1 in her apartment with another guy at night
Why aren't you comfortable with your girlfriend having guy friends in her apartment?
I don't feel satisfied with it. It concerns me
Even if she is not doing anything wrong, it is not good that she is not taking you seriously. It could hurt the relationship to try not to work and compromise on stuff.
The only guy she should be seeing is me.
The situation is suspicious but you should first learn about the guy friend to see if they really are just friends. Let her know how uncomfortable it makes you feel and she'll notice your concern.