These are the details of Jacob's relationships before and during the series.
Chelsea is Jacob's ex-wife. They met in high school while Jacob still had feelings for Quinn but figured it was time to move on and dated the cheerleader. Following high school graduation Jacob married Chelsea and moved away to play both college and professional football, but their marriage was anything but happy as Chelsea would boss Jacob around and banned him from speaking to Quinn. Eventually Chelsea cheated on Jacob and Jacob filed for a divorce from her.
Quinn was one of Jacob's childhood friends and his first crush. Jacob fell hard for Quinn when he met her and vice versa. Quinn had always made Jacob feel special and does not like it when he labels himself as a psychopath when he lets his anger lose. For a few days just to get away from his parents arguing he would spend the night with Quinn and her family while they lived in Tree Hill. Both Jacob and Quinn's feelings for each other grew and grew while they were growing up to the point where they were attached to each other. For one of Jacob's birthdays Quinn paid Jacob a visit and gave him a present which was a picture of her, Haley and Taylor. After graduating high school the friends went their separate ways while Jacob married Chelsea and moved to Baltimore to play for the Baltimore Ravens Quinn left Tree Hill and dated a guy named David despite still having feelings for her best friend and crush Jacob. In season one while Jacob returned to Tree Hill Quinn followed him after she and David divorced and wanted to admit she was in love with him and marry him. While during the cafe shooting while Jacob and Haley were trapped with the shooter inside the cafe Quinn rushed down to see what was happening and heard the gunshot inside the cafe but was not aware that it was Jacob who was shot until paramedics arrived after Quinn's sister called Haley called them over to have Jacob be treated at the hospital and then eventually followed the ambulance. Several days after the shooting Jacob woke up and was taken home to Quinn's parents house because of the fighting going on at home and allowed him to rest in her bed while Quinn slept on the couch. At the beginning of season two Jacob moved in with Quinn until they could afford a house together. Once Jacob left the cafe to work at their former high school fulltime Quinn took over his job and worked alongside Haley and Lucas. By season three Jacob and Quinn are engaged and plan on having the wedding at Haley's graduation as her present. Quinn alongside Haley and Brooke seems the be the only people who can calm Jacob when he is angry and is about do something stupid. Quinn admitted that was extremely heartbroken when Jacob married Chelsea but forgave him as she always knew Jacob still truly liked her deep down.