Why Do We Always Remember The Good, And Sometimes Forget The Bad?

I look back at my past relationship and for a long time, I wanted it to work so badly, that there were times that he hurt my feelings terribly, and I would eventually go back with him, forgive him and all of a sudden, I was missing the "good" in us and not focusing so much on the "bad". Why do our minds let go of the bad when they cheat on us? Or perhaps it's not our minds, but our hearts that are taking over. I believe that there are many times when our hearts want one thing, and our minds want something totally different. Love can be so hard sometimes. I am very glad that I was strong enough to walk away, especially after having it happen over and over again....it would have never stopped. He was just way too interested in having more than one woman. I look back now and wonder why I put up with it for such a long time.  I know that it had to have been my heart holding on for so long, because my mind knew better, but the heart won out for it seems like forever. Today I am happy and a much stronger woman. Being in love is wonderful, but when you start getting cheated on, your life just seems to fall apart. Onward and Upward for me.....and have I forgotten the bad that he put me through?  No, but it has faded more back into the memory bank and today I am thankful for having been able to finally move on.