Coincidentally, I am also a Cancer, and my boyfriend is also a Sagittarius.
So I can understand some of her psychology!
She actually relies on you and clings to you because she likes you very much. She looks fierce on the surface, but in fact she is not really fierce~it’s just a superficial appearance!
She felt that if she was too good to you and too clingy to you, you would annoy her, so she began to arm her heart with the shell of too much.
As for the previous person, he probably doesn’t like it anymore, otherwise she wouldn’t choose to be with you.
But she is nostalgic, and she feels that she can still be friends even if she cannot be lovers.
So just treat him as a friend! !
In fact, women are sometimes easy to coax.
Cancer is a zodiac sign that easily feels insecure, so you should always tell her you love her, say you won’t leave, and stay with her as much as possible.
Slowly you will find that what you get in return will be more than what you paid for her.