It is all about her anxiety and mistrust and she maybe feel low sense of self-worth.She maybe gets paranoid due to past experiences.
Dealing with your gf requires a lot of patience, compassion, and strong personal boundaries since she mostly seek endless assurance from you.Encourage her to open up and voice her thoughts and be sure to listen in and know how to react in a non defensive way and never argue with her.Always have an open convo just to show there is no reason to be paranoid.All you need to do is to empathize her feelings.
Don't be rude to her,instead support her and understand what she's going through.You just need to ease her mind ,to be free from doubts.If you still both want to save the relationship,you just need to have an open heart & mind.Or if you feel you're exhauted ,why not take a break and give some space to clear your thoughts.