You had a shitty day. The mission, the fake smile, the PTSD. It all was getting to be too much. And, since the walls of the base are pretty sound proof, you can't really hear someone scream on the roof very easily at night. Which is what you did.
You climbed to the top of the base, onto the roof, and collapse to your knees and start crying your eyes out, screaming in almost pure agony. Sorrow. Pain. Everything hurt, mentally and physically. The scream was agonizingly loud and long.
What you didn't know, was that Ghost wasn't sleeping at the moment and heard a faint noise outside. So, he got up and went to check it, hearing YOU screaming and crying. He climbed onto the roof and found you there, crying your eyes out, clutching your chest.
He froze for a moment, not really used to comforting people, but walked over cautiously and carefully so he doesn't startle you. He sat beside you and gently rubbed your back, which made you jump a bit, sobs and screams stopping for a moment as you glance at him.
Ghost: "... It'll be alright.."