To my breaking point

So this past week it seems as though me and my boyfriend of three years have been having some serious issues. Today I finally got him to tell me how he felt. I told him that I felt like I'm being pushed away. He stated that I always seem like I'm pissed off about something everyday and he is tired of it and my complaining and that I'm always on his ass. But to me, he's been so snappy with me and I feel like I can do nothing right. I really don't know how to make this situation better. I told him today that there would be no fighting between us anymore. I just need advice and inputs on what you would do in the situation or how to make things better?