You remember the good things because you are looking for validation and comfort. At least that is what I think it is for me. I need to know I wasn't stupid for giving him myself, my trust, my love, my hope and that I was a little more important. Addicts don't think like non-addicts. That is hard to remember and comprehend. What seems red to us can seem black to them. I miss my A too sometimes. Now however, I have seperated those good times to someone that doesn't exist anymore. I can also think of 10 bad things for every one good that comes from the person that I know now.
It will get easier, hang in there, stick with us, we will help you. Hugs.