Answer:
Over estimated
Under estimated
Explanation: To estimate or make an estimate means to try to guess or measure the extent at which something is. For example when you guess how big a box is by merely looking at it without actually measuring the box to know exactly how big it is. You re making an estimate of the size of the box.
In this context, at first when they started dating, they didn't realize that they love each other less than they actually do, which could be why they broke up. They overestimated how much they liked each other.
Then when they broke up, they thought that they thought they didn't even like each other at all. They underestimated how much they liked each other.