My mom is a Sagi and am related and know quite a few Sagittarians. They do not like people being jealous or possessive of them. They need their freedom and no matter how much trying to impress her or trying to win her back won’t help.
My mother had a problem with this with her ex-boyfriend and it made her pretty upset. She absolutely wants nothing to do with him and refuses to talk to him ( which I don’t know her because of his control issues).
Having jealousy issues or being possessive is insecurity. Afraid that a partner will leave that person for someone better. Have you ever had problems with your self-esteem or an issue from your past that has developed into jealousy and being possessive? Something that hasn’t directly been dealt with.
I think in my personal opinion and you don’t have to pay heed to it, you should try and focus some on you. Give things a chance to settle and let your ex-girlfriend a chance to settle down as well. I am a huge believer in the No Contact policy after a breakup. If a relationship never worked out than it isn’t meant to be.