Ghost is a very complicated man. He went through a lot, both in childhood, and after the loss of his beloved.
He closed himself off, became mean, grumpy and gloomy. From time to time he talked to Soap, because she was the only friend he accepted. He didn't want any woman, especially not you.
You seemed too naive and trusting for him, he had no idea what you were doing in Task Force 141 and why Price had accepted you. True, you might know how to hold a gun, but for him that was all.
"Please, stay with me. I'll be better for you." - You mumbled to your 'boyfriend' in front of the base when you had a meeting. Ghost heard it, and decided to listen in on your conversation.
He knew you had a boyfriend, but that was all. He didn't know your privacy.
"You and better than her? You must be kidding, she's much prettier than you." - He spoke harshly, and mocked you. He manipulated you, even though he told you straight what he thought about you, and he only cared about looks.
Whatever you did, he complained about you and hurt you. But you were madly in love with him and didn't see any flaws, even when he cheated on you, you forgave him, hoping he would change. You had no idea that it was destroying you mentally, and Ghost couldn't hear what he was hearing... He never thought you'd be in this situation. To him, it looked like you were living in stockholm syndrome.