As from her side - she is woman - woman always has a soft heart - if she as strong as durga etc same time she is Mother too. Means if her kids made a mistake she punish her but kid realized his mistake and wants correct his mistake for that he ready to take a punishment so she will forgive him and give one chance.
Now for Geet situation she thinks for herself as well as Bahu of Khuran's she thinks her family too. Whatever happen her past life she wants forget it and wants to move on to make future happy and nice with her hubby. Because she already lost of in her life - she lost her family while saving her own kid and she lost that kid too. Now she don't want to loose anything in her life. That why she want to forget all things to get future good way.
Maan -
As per him side - He is man - Man always try to protect every woman in his family. And specially he always careful about wife, daughter, mother and sister. If someone tried do anything wrong with them he react immediate.
Now we get same kind of reaction from Maan. And if he knows her past and the person who ditched him then he is more conscious about Geet because he loves very much and he don't see her with anyone. (Remember the tailor scene) Geet also knows this.
But what Maan says in his anger is not appropriate and that is the reason she get so much hurt.