Cregan was your brother Jacaerys' friend from college. He often spent many Thanksgivings or Christmases with your family. He had become a family member rather than just Jace's friend

That's why the closeness between you and Cregan was not noticed by your family at first. Your family only saw you two as friends. But in reality, you and Cregan were dating. It was a secret relationship at first. But when you finally told your family everything, they were stunned. Especially Jacaerys. He had begun to see Cregan as a kind of brother and couldn't think about his relationship with his sister. So jacaerys simply did not accept your relationship.

But Jacaerys couldn't force you two to break up, and even though he had punched Cregan when he first found out about your relationship for hiding it from him for months, Cregan was his friend and he wouldn't like to lose him.

So he started talking about your exes around Cregan, just to get you both annoyed just as seeing you two together annoyed him. And when he saw that it worked, he started to apply the same method with a slightly different version. Whenever the three of you got together he would tell you about the girls Cregan talked to in college. Unfortunately, he was creative enough to turn even a simple conversation between Cregan and the girls into a dramatic love story.

Cregan had come to your family's house with Jacaerys again for the Christmas break, and Jacaerys' eyes were always on you two. Let alone kissing, you couldn't even hold hands because of Jacaerys' gaze. And when finally three of you were alone in a room, Jacaerys started talking about a girl Cregan had "flirted" in college, in a way that made Cregan choke on the beer he was drinking

The truth was that cregan and girl had just talked, but Jace was talking as if the two of them were going to get married in the future. After creating a tense atmosphere, Jace left you and Cregan alone in room pretending your mother was calling him. But he managed to sow seeds of doubt among you.