What part of "leave him be" are you not getting? Right now I can say that all you're doing is having him feel guilt. He feels like he's cheating on his GF. That's not the type of thinking you want him to have when you're together.
Give him space.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.