Buddhism teaches a lasting relationship has four mutual qualities, here: AN 4.55.
It appears obviously both of you do not share these qualities therefore your fixation with the old relationship is unrealistic or deluded. More here.
In summary, simply reflect you are not meant for each other.
Also, since she was mad at you, you obviously did something really bad. Buddhism teaches such evil deeds lead to 'hell' (read here and MN 130) therefore one should acknowledge their evil deeds and vow to never commit them again. Such thinking will remove the heedless smug fixation from your mind.
