Overreacting is what I did too, and I did not know how to stop. I broke up and went back with him so many times, always looking for that time at the first of our relationship that was so wonderful.
It does not help that your body is going through changes, but the mind controls the body. Now you have to control the mind. You have to get to a point where you are with him because you want to be (or anyone else for that matter) and not because you can't live without him.
I believe your problem is not basically physical, although that is a contributing factor, but emotional. Post your situation on the relationship and women's forums and let some of those wise women help you.