I can't play online anymore

Hi, I just returned to Halo because my friend wanted to play tonight and we were having a blast until after a game it kicked us back to the lobby for choosing a game mode. Every time I try to start a game, I see the ‘‘Searching for players…’’ for 1 second and it kick me back out. My friend then proceeded to quit my squad so I can try to re-invite him and when I invite him through the game, he doesn’t receive the invitation, and when I try to invite him through the Xbox Menu, the options to invite him in a game are grayed out. What is going on?

Is your NAT type open?