Harper was killed by Jack before he and Jennifer were even officially a couple, really early days of Jack & Jenn. Laura being the mother would make no sense since Abby was already a few years old by the time of that affair, plus Laura was already pretty old by then and as said, she was never pregnant afterwards. Even if she had an abortion, that would take some major rewrite of history (not that that hasn’t happened before) The thing about Jack’s back story, he came to Salem for two reasons, one to get treatment for Hodgkins Disease (he was actually dying from it) and two because he was looking to reconnect with Kayla who he had a vacation fling with years before while on vacation in Hawaii. A little “summer lovin'” if you will. Doesn’t mean Jack wasn’t a playboy in his youth. But if this was right before he came to Salem, it seems he was in bad health at that time which wouldn’t make sense for him to be living the playboy lifestyle while your dying. Also, I’m pretty sure he lived in Washington, D.C. before coming to Salem since his father was Senator and was campaigning for the Presidency.