Ashley Seaver and Spencer Reid had been secretly seeing each other for about a year. Both seemed to be fascinated with each other's family history. Seaver's father was a serial killer. Reid's mother was mentally ill. Both of them had decided that they didn't want to have any children. They had never actually discussed this at length.
About seven months after secretly seeing each other, they became intimate with each other. Shortly thereafter, Reid started to develop severe headaches. They got worse until 4 months later; he went to the doctor because he couldn't stand the pain any longer. A cause wasn't found but the doctor gave him two medications which helped him a lot. The headaches stopped but the side effects of the medications put an end to their sex life and their relationship. Reid had never told her about the headaches or the medications he was talking.
Reid forgot to bring his pills on a trip. He noticed that he didn't have any headaches and the BAU was away for nearly four days. In fact he had no headaches at all. He decided to stop taking them.
Hotch had noticed that the relationship between Seaver and Reid had changed. They had gone from talking to each other all the time to barely talking to each other and avoiding each other as much as possible. Others had noticed it. When Hotch took them aside, they said everything was fine but Hotch knew otherwise. He'd figured they've had a falling out over something.
After a year and a half Ashley Seaver left the Bureau. Reid was relieved that he didn't have to see her everyday at work. Their relationship was one that he wished had never happened and if he had to do it all over again, he never would have gotten close to her. Despite his thoughts, he still had a strong physical attraction to her that he tried to deny.
The next chapter will be about Ashley's Seaver's 30th Birthday Party.