I really want to tell him how I feel but I'm to scared. I'm a snake.

From the aspect of zodiac compatibility, the compatibility between you and he, he and his GF is almost the same. It's true that they argue very often. But they haven't broken up. If you really love him, you should hide your love and see if you can do something to make them two more harmonious. If he realizes that his relationship should end, then you may confess your love to him.