Okay So every time I play through New Vegas Lt. Monroe seems to disappear after he gets to Camp Forlorn Hope at first I thought he was being killed but it seems he just disappeared. I came to Forlorn Hope later in the game and say that he was gone so I was like no big deal I'll just load the save I made a little bit ago while I was in Camp Forlorn Hope standing right next to him. So I did and when I did he was still gone. So I came to the conclusion he just likes to disappear.

I know this is an odd topic to start but if your like me and want to keep as many named NPC's alive this will probably tic you off a bit but at least you know he didn't just die.

Who is Monroe? Is that the guy at Boulder City?

Yes.

Lt. Monroe is the OIC at Boulder City during the hostage event. http://fallout.wikia.com/wiki/Monroe